Editor's Note: This growing directory is manually maintained by a physicist whose interests cover also mathematics, chemistry, ecology and environment, electronics and philosophy of science. It is therefore inevitably biased towards such interests. The page is automatically tested for broken links once a month and links which appear broken for three or more consecutive months are deleted.

Should there be anything wrong with an entry, let me know and I will be glad to correct it.
Note: an entry can appear in several categories.

Hint: the F's in this table point to lists of free texts:

NEWS, eZines, Magazines, Journals, Blogs, ...

• BBC Nature news.
• BBC Science news.
• Discover magazine news.
• Nature magazine.
• New Scientist magazine.
• Physics Forums and its Insights, guides, iutorials, interviews, ...
• Sceptic. magazine.
• Science4All magazine. Nice popularization articles.
• Science Daily news.
• Science & Development Network (SciDevNet). News & views regarding developing countries.
• Science News online.
• Science magazine.
• Sciencebase by David Bradley.
• Scientific American magazine.
• SEED magazine news.
• TechDirt. Technology oriented critical news.
• The National Academies Press.
• WSEAS, World Scientific and Engineering Academy and Society.
• Free trade magazines
• Engineering Research Library maintains a huge list of resources, sorted by category.
• Notizie e Riviste Italiane
• University, il Portale degli Universitari.
• Le Scienze.
• Newton.
• OggiScienza.
• UniversiNet. Un e-zine degli univeritari Italiani.
• Journals and publication searches
• arXive. A huge repository of free science articles at Cornell University.
• BioMedSearch. Biomedical search engine containing NIH/PubMed documents,
  plus a large collection of free theses, dissertations, and other publications.
• Budapest Open Access Initiative (BOAI). Editors and scientists: Join this movement!
• CERN Document Server, a huge, open-access repository of articles, theses, ...
• Directory of Open Access Journals (DOAJ), managed by Lund University Libraries. Great!
• EUREKA, the Science Journal Watch. You must read this.
• Science Direct, an entry gate to over 1800 journals.
• PubMedCentral. A huge repository of free life-sciences articles at NIH.
• Blogs:
• Excel Hero blog, a great place if you use Excel.
• Mathematics Journals blog of John Ewing. Great reflections about scientific publishing.
• Science blog of David Bradley on his Sciencebase.
• Science Blogs, a roof science blogging system.
• The Document Foundation blog, covering Libre Office.
• The Scientific Activist, now hosted by Science Blogs.

EDUCATION, free online books, and plain fun

• arXive. A huge repository of free science articles at Cornell University.
• Computer History Museum, a great place to visit.
• Centre for Bioscience of the Higher Education Academy.
• Center for the Popularization of Mathematics (CPM) at Uni Wales, Bangor, UK.
  Great, especially on knots and sculpture.
• Climate Change Education. Global warming, climate change and solutions.
• edHelper. Science stuff for kids and their teachers.
• Electronics Tutorials. Recommended categories: basic electronics, kits, humour.
• Higher Education Academy. A UK academic educational support initiative.
• History of Chemistry. Collection of links, including history of science in general.
• Hubble heritage project. Don't miss the image gallery page.
• Hubble telescope site. Have a look at their Fun & Games page.
• Images of the Sun from SOHO. Near real time and historic.
• Images of the Earth from EUMETSAT satellites.
• Images of the Earth from GEOS.
• Khan Academy, open-source science videos (9000+) and lessons. Amazing!. See also.
• Math and Reading Help for Kids, a nice directory of math-education articles, games, etc.
• Math for the Left and Right Brain, to teach kids (pre-K to ninth grade).
• Medical Site online books (by specialty).
• MERLOT. An amazing educational resource.
• NASA/Spacelink. It's a vast space out there ...
• Near Earth Objects watch. Will a big one hit us soon ?!
• Nobel Prize Organization Outreach Program.
  A growing set of Games, Simulations and Readings pertinent to various Nobel-grade discoveries.
• NTEN National Teachers Enhancement Network. Science education.
• PubMedCentral. A huge repository of free life-sciences articles at NIH.
• Scitable Learn about Genetics at Scitable from Nature Education.
• Smithsonian Institution. Museums + much more.
• Solar eclipse video available at the Pakistani Khwarzimic Society web site.
• Sky almanac for skygazers at Star Date magazine (Texas).
• The Science of Spectroscopy for the advanced.
• Views of the Solar System collected by Calvin J.Hamilton.
• Virtual Math Museum maintained by R.Palais. Amazing.
• Vision Laerning, a great site for teachers and pupils alike. Go first to Library.
• WorldWide Telescope, a nice initiative by Microsoft Research.
• Free Online Books, Courses, Lectures and other Texts
• Cornell University Library Windows on the Past. An excellent open-access resource.
• Course Correction report from Make Textbooks Affordable. Interesting.
• Directory of free online Books. Crammed with ads, many links are broken or point to garbage
  (e.g. old Company manuals) but worth browsing when you have a lot of time.
• Free Books with accent on mathematics, programming and computer science.
• Free online Classes listed on Guide to Online Schools. A great list.
• Free online CHEMISTRY books. Manually selected and checked links.
• Free online ELECTRONICS books. Manually selected and checked links.
• Free online MAGNETIC RESONANCE texts. Manually selected and checked links.
• Free online MATH books. Manually selected and checked links.
• Free online PHYSICS books. Manually selected and checked links.
• Free online SOFTWARE development books. Manually selected and checked links.
• FreeScience directory of over 1500 free, online books.
  Very valuable resource, though it counts as books also courses and scripta.
• Gallica, bibliothèque numérique. Huge collection of historic books.
• Internet Archive texts and audio-visuals. See the Open Library.
• MIT Open CourseWare initiative. Free courses and books.
• Project Gutenberg initiative. Over 39000 free online books.
• Scribd, a huge books and documents database. You must subscribe, but it is free.
• Tech Books for Free. Free books on technology subjects.
• TextBook Revolution. Students and teachers, don't miss this one!
• Web Teaching, an online book about how to teach through Internet written by David W.Brooks, Diane E.Nolan and Susan G.Gallagher. 2nd Edition (2000). A bit old but excellent.
• Fun, poetry, stories, ...
• Annals of Improbable Research. This is fun.
• Bizarre Stuff. You can make it in your kitchen.
• Consciousness, Physics, and the Holographic Paradigm.
  by A.T.Williams. Unusual, stuffed with links and poetry. Worth pondering.
• Crystal Radio. Crystal radios, kits, parts, and supplies for the radio enthusiast.
• Excel Hero blog has cool optical illusions to run in Excel. With demos.
• Eye tricks. Most amusing.
• FunFacts at Harvey Mudd College. Have fun with Math!
• Geek stuff shop. See air-zooka, romp pendulum, etc...
• Mathematical Art at the Virtual Math Museum. Amazing.
• Phun Physics from the University of Virginia.
• Science poetry & fun corner in Stan's and Lucia's Log Cabin.
• Science poetry inspired by Space exploration by Stuart Atkinson.
• Science Songs by Greg Crowther et al. See also his science songs links.
• The Ultimate Guide to Optical Illusions. Nice.
• Trivia Facts and Quizzes.
• WokJoke, a huge collection of nice jokes.

DICTIONARIES, Encyclopedias and Wikies

• BABEL. On-line Glossary of Computer-Oriented Abbreviations and Acronyms
• Concise Encyclopedia of Mathematics by Eric Weisstein, at Mathworld of Wolfram Research.
• DADS. Dictionary of Algorithms and Data Structures at NIST.
• Dictionarist, a multi-lingual, talking on-line dictionary.
• Dictionary.com, dictionaries, thesauruses, flashcards, interactive translators, ...
• DiracDelta, a Science & Engineering Encyclopedia.
• Educypedia. An educational encyclopedia.
• Encyclopeadia Britannica.
• FOLDOC. Free on-line Dictionary of Computing.
• Internet Encyclopedia of Philosophy at UTM.
• Mathematics Dictionary & Glossary for students.
• Medline Plus. NIH medical encyclopedia.
• Merriam - Webster Online. One of the best english dictionaries.
• Microsoft Encarta Dictionary.
• Microsoft Encarta Encyclopedia.
• Stanford Encyclopedia of Philosophy.
• Tech Encyclopedia centers on Informatics and Computers.
• Technical Library online. Concentrates on electronics.
• TechWeb Encyclopedia.
• The Worlds of David Darling. Astronomy, Space, Alternative energy, Sustainable living.
• Units of Measurements Dictionary by Russ Rowlett at UNC.
• Weisstein's Dictionaries (by Eric Weisstein).
• Word Reference. A multi-language dictionary (English, French, Italian, Spanish).
• Word Reference italiano, inglese, francese e spagnolo.
• Wikies
• Webopedia Free Web-based computer encyclopedia.
• Welcome to Exploring Science is a wiki for teachers.
• Wikipedia Free Web encyclopedia.

DATABASES and Link Directories

• The three heavyweight DataBases (permanently interconnected):
• CAS, Chemical Abstracts Services, a division of ACS.
• eFunda, the ultimate reference for Engineers.
• STN, Science and Technology International, located un Germany.
• JST, Japan Science and Technology Agency.
• ... and the others:
• AIST database (Japan). Very good and free.
• CERN Document Server, an open-access repository of articles, theses, ...
• arXive, huge repository of free scientific articles at Cornell University. See also Front for arXive.
• Chemdex. Huge chemistry Directory at Uni Sheffield (by Mark Winters).
• Chemistry Thesaurus. Free and excellent.
• Chmoogle. A google-like chemistry database.
• CODATA, Committee on Data for Science and Technology.
• Constants of Physics and Mathematics.
• Engineering Fundamentals database.
• FreeScience, a directory of over 1500 free online books.
  Very valuable resource, thought it counts as books also courses and scripta.
• Genome Gateway. Genomics links, references, data, ....
• HyperPhysics. An amazing physics database at Georgia State University..
• NIST Chemistry Webbook (chemical data).
• NIST Physical Reference Data (physical constants etc).
• Scribd, a huge books and documents database. You must subscribe, but it is free.
• SI Units and Prefixes.
• SI Dimensions of Physical Quantities. Over 200 quantities in 22 categories.
• Universal Nuclide Chart from Nucleonica (a site maintained by the EU).
• Link directories and Search engines
• BUBL Link. An amazing collection of links, each with a brief description, at Strathclyde University.
• WebRing of Science.
• Search Engines
• DMOZ Open Directory Project. The largest human-edited directory.
• One Look has a very interesting approach.
• Scirus is dedicated to sites with scientific information.
• SciSeek has an very rich set of categories.

Climate Change, theories and practice

• Azimuth Project, a serious international collaboration.
• Climate Change definition on EcoLife.
• Climate Change on Wikipedia.
• Real Climate. Climate science from climate scientists.
• Glaciers and Global Warming. A small photographic testimony from Stan (Italian-French Alps, 2007).

SOFTWARE: free/low-cost Utilities, Calculators, and Help

• Calc98, pretty good and free multi-mode calculator.
  There is also a reduced-functionality online version (jCalc).
• Calculator++, a cross-platform (Java) arbitrary-precision calculator.
• Derivative Calculator from David Scherfgen. Online symbolic derivatives. Nice.
• Digital Dutch web converter for basic physical quantities by J.D.Stegeman. Simple and elegant.
• Excel Hero blog, a great place if you want to really use Excel.
• GNU Free Software Directory, free, serious, official. And GREAT.
• Googol+ from Atelier Web is real great if you need an arbitrary-precision calculator.
• Libre Office, free, open-source, Intel-backed outgrowth of Open Office
  maintained by The Document Foundation. See their blog. NEW & GREAT.
• MathStudio a great low-cost graphing and symbolic math app for mobiles and Windows.
  Goes also under the name SpaceTime.
• Open Office, free Microsoft Office competitor. Now hosted by Apache Software Foundation.
• Smooth Draw. Comfortable Utility for free-hand drawing.
• Software 995 a range of free / low-cost handy utilities.
• Windows calculator from Tvalx (free) accepts editable formulas and remembers session history.
  Standard Windows Copy/Paste, but does not do symbolic math (numeric data only).
• On-site links to more software tools and utilities:
• Stan's Software Development and IT Links,
  with a list of sci-tech tools and file-management utilities.
• Stan's Mathematics Links, with a list of handy tools and math utilities.
• Stan's Physics Links, with a list of utilities for physicists (but not only).
• Stan's Chemistry Links, with a list of utilities for chemists (but not only).
• Stan's Electronic and Electric Engineering Links, with a list of utilities for electronic engineers.

STANDARDS and Norms

• AIST National Institute of Advanced Industrial Science and Technology (Japan).
• ANSI American National Standards Institute.
• ASQ American Society for Quality.
• ASTM International. Formerly American Standards and Measures.
• BIPM. The home page of the SI System of Units. English version.
• CEN Comitè Européen de Normalization (European Committee for Standardization).
• CODATA Committee on Data for Science and Technology.
• DOE Fundamental Standards at the HSS (Office of Healths, Safety and Security).
• EA European co-operation for Accreditation.
• ETSI European Telecommunications Standards Institute.
• FDA US Food and Drug Administration.
• FCC Federal Communications Commission (USA).
• IEC International Electrotechnical Commission.
• IEEE standards.
• ILAC International Laboratory Accreditation Cooperation.
• IQA Institute of Quality Assurance.
• ISBN International Standard Book Number. They assign the numbers.
• ISO International Organization for Standardization.
• NIST. National Institute of Standards.

Low-cost INSTRUMENTS for Education & Home Science

• Cenco Physics. An educational and home-science instrumentation supermarket.
• MatchRockets. Experimental Science for everyone.
• Ocean Optics. Affordable VISIBLE, UV and IR spectrometers and optics.
  USB instruments. Look up spectrometers for education.
• Physlink Science e-Store. Science gadgets for kids. Great.
• PV Scientific Instruments. Reproductions of historic instruments.
• TeachSpin. Small instruments for teaching Science.
• TelAtomic. Small instruments for teaching Science.

HISTORY of Science

• Charles Darwin online. Complete works.
• Cornell University Library Windows on the Past.
  Excellent open-access resource.
• Epact: Scientific instruments of Medieval and Renaissance Europe.
• Gallica, bibliothèque numérique. Huge collection of historic books.
• History of Chemistry links on this site.
• History of Computing links on this site.
• History of Magnetic Resonance links and references on this site (NMR, MRI, ESR, NQR).
• History of Mathematics links on this site.
• History of Physics links on this site.
• History of Russian Science and Technology. A huge virtual guide at MIT.
• History of Science Society.
• Nuclear Files. A project of the Nuclear Age Peace Foundation.
• Marian Koshland Science Museum of the National Academy of Sciences. Not just history.

PHILOSOPHY of Science, Epistemology, ...

• American Philosophical Society.
• Carl Gustav Jung, the human mind explorer.
• Consciousness studies at Uni Arizona. Quantum-mind !?
• Dharma Haven. Wary as I am of oriental spiritualism, I find this site actually quite good.
  Especially the essays about Western Science by Terry Halves.
• Dmytro Taranovsky. An eclectic scientist at MIT.
• Episteme Links, a great links collection by Thomas Ryan Stone.
• Guide to Philosophy on the Internet by Peter Suber.
• HYLE, International Journal for Philosophy of Chemistry. Open access.
• Internet Encyclopedia of Philosophy at UTM.
• Is Life Improbable?, an article by John C.Baez.
• Karl Popper at the University of Klagenfurt site (Austria).
• Philosophy around the Web by Peter J.King.
• Philosophy of Science Archives at University of Pittsburg.
• Philosophy of Science Links collected by Peter J.King.
• Philosophy of Science Resources collected by B.Janz.
• Philosophy related Resources at University of Liverpool.
• Popper, Bayes and the Inverse Problem by Albert Tarantola
• Quantum Theory and the Bayesian Inference Problems by Stan Sykora.
• Science and pseudoscience: how to tell the difference, by Stephen Lower.
• Stanford Encyclopedia of Philosophy.
• Symmetries and Reflections, an essay by E.P.Wigner.
• The American Philosophical Association.
• The Critical Rationalist journal.
• The Huxley file, an online book about T.H.Huxley by Charles Blinderman and David Joyce.
• The Philosopher. Electronic version of the Journal of the Philosophical Society of England.
• The Philosophy of Science Association.
• Understanding Science portal at Berkeley.
• What are the best philosophy resources?.

SANDBOX for items yet to be sorted

• Wikipedia: list of effects.