After 20 years, Stanford Encyclopedia of Philosophy thrives on the web
news.stanford.edu
news.stanford.edu
I've even turned to SEP for mathematical concepts (to the extent it covers math), for example, because there is no free authoritative resource in that field.
Does http://mathworld.wolfram.com/ not do the trick for what you were looking into?
Compare, for example:
* http://mathworld.wolfram.com/ModelTheory.html
* http://plato.stanford.edu/entries/model-theory/
EDIT: Replaced the examples with better ones
http://wikipediocracy.com/2013/10/20/elementary-mathematics-...
If you don't already know what you are reading, you can't distinguish knowledge from nonsense.
I'm personally a much bigger fan of curated/academic encyclopedias like SEP as opposed to open encyclopedias (Wikipedia, etc.) so it's good to see it thrive.
Scholarpedia
In the years just prior to Einstein's publication of his Special Relativity theory Dutch physicist Hendrik Lorentz showed using Maxwell's equations for the electric fields within an object of distributed charge density that the fields would produce inertia in proportion to the object's electric potential energy content...
Wikipedia
In theoretical astrophysics, the Nordtvedt effect refers to the relative motion between the Earth and the Moon which would be observed if the gravitational self-energy of a body contributed differently to its gravitational mass and inertial mass. If observed, the Nordtvedt effect would violate the strong equivalence...
The complete Wikipedia article is much smaller than many, but while the Scholarpedia version is much more complete, it takes a long while to get anywhere.
Edit: expanded, changed format.
I'm curious how being invited or accepted to write an article on topic affects academic prestige and tenure decisions. Is Brian Orend who wrote http://plato.stanford.edu/entries/war/ considered the canonical living expert on the philosophy of war?
I'd love to know more about the incentives and culture around this. I'm sure there are many insights one can draw about building valuable evolving repositories of knowledge from recognized exports.
One hint may be in http://plato.stanford.edu/info.html#policies
"Contributions to the Encyclopedia are normally solicited by invitation from a member of the Editorial Board. However, qualified potential contributors may send to the Principal Editor or an appropriate member of the Editorial Board a proposal to write on an Encyclopedia topic, along with a curriculum vitae." "By qualified, we mean those persons with accredited Ph.D.s in Philosophy (or a related discipline) who have published refereed works on the topic of the proposed entry..."
Also perhaps http://plato.stanford.edu/info.html#copyright . I don't know how much non-cs academics think about copyright and licensing, but as most accomplished academics are authors, I am guessing it may matter to them that they keep ownership.
"Copyright Notice. Authors contributing an entry or entries to the Stanford Encyclopedia of Philosophy, except as provided herein, retain the copyright to their entry or entries. By contributing an entry or entries, authors grant to the Metaphysics Research Lab at Stanford University an exclusive license to publish their entry or entries..."
This is just one facet of course. I'm sure there are many other factors such as possibly the stature of the Stanford lab, and particular personal relationships and technical skill of those involved, good timing, etc. I'd be very curious to hear from those with personal knowledge of the details.
That said, I think writing an SEP article is a nice line item on a resume but not the sort of thing that makes your career. I think the authors typically write the articles after receiving some recognition.
Most SEP articles seem to have been written by younger professors (mostly in their 40s) whose daily job is to teach balanced, comprehensive, introductory courses on general topics. They might not be world-class experts in any single field, but they have broad knowledge and teaching experience. They might have edited anthologies or organized conferences on the topic. They know what points students are prone to miss. They know which theories are frequently misunderstood. This breadth, not depth, makes them ideal authors of encyclopedia articles.