A wiki for creating virtual worlds, it contains 3d models, textures, sounds, motion capture data, concept art, sprites, etc. under Free content licenses.
There are a lot of models that are "standardized" or that include some "standard" piece. For example cars, trains, airplanes, computer hardware, a lot of everyday objects ect. These models don't need to be remodeled for every project, they can be modeled and improved like free software.
WikiWorlds aims to be a repository of free game character, levels, weapons, worlds not tied to an engine, like an encyclopedia for free game media.
There are just few pages here and there with free models and textures and most often with licenses that are not really free as in speech or too unclear to be "safe".
There are sites with a lot of good proprietary content which contains some free stuff, but with unclear licenses too.
Often artists publish free media on their personal sites, without a categorization system and with unclear licenses.
A lot of content for commercial games is created by players but it is often distributed under restrictive licenses (no derivative works allowed, no redistribution etc.) and in a format tied to the game engine.
At this time there is not a single place to upload all the free media. This wiki collect all this material in a single place and categorize it.
Why a wiki Edit
A wiki is more flexible than a traditional CMS (content management system). There can be a lot of relations between articles and media files that can't be foreseen. And the management of the wiki will be done by users so it's more scalable. MediaWiki has a lot of features to manage media files (wikimedia commons is an example).
MediaWiki has features to categorize, to comment pages and media files, to create and coordinate groups of people that works in a subproject and to search content built-in. It can be extended with plugins.