As a slight addendum to the above, several things have changed since 2002 for the [Wikimedia Foundation] (WMF). Possibly the most relevant is that there are now a few more sister projects. In addition to background [wiki]s which are of little interest to the general public (e.g. [Meta-Wiki], which is discussion of the WMF projects themselves and [MediaWiki], which develops the software that runs all of the other projects), there are:

[Wikispecies]: a [taxonomy|taxonomic] directory of species. This is mostly populated by specialists but everyone can add something to the project.
[Wikiversity]: spun off from Wikibooks, this is for more general learning resources than a strict textbook. E.g. there is a [bloom clock] that has been gathering data about when certain species of flower bloom around the world. Wikiversity encourages original research, unlike Wikipedia.
[Wikidata]: structured database. Part of the reason for creating it was to synchronize some basic data (e.g. dates of birth) across the 275 or so language editions of Wikipedia but it also got a huge boost from inheriting [Google]'s [Freebase] and has millions of data items. Due to a particularity of licensing for databases, it is the only project whose contributions are in the [public domain] by default. Also, its interface is [JavaScript] heavy and you don't interact directly with pages but edit database entries instead.
[Wikivoyage]: a free travel guide. Like [Lonely Planet] but updated in real time by travelers all over the globe. This appears to be the newest project but it was actually adopted by the WMF in 2013 after having been a fork of [Wikitravel], which was founded in 2003 by some Wikipedians who wanted to make a more reliable and up-to-date travel guide.

All noders are invited to participate in all projects—you all have something to give.

As a post-script, I would be remiss if I didn't mention the only retired WMF project: 9/11 Memories. This was made shortly after the [September 11th] attacks and was a kind of discussion board, memorial, and general dumping ground of public memory about 9/11. It was closed after a couple of years and was eventually removed from almost all references. Never forget.

Wikipedia (thing)