The alternative to Wikipedia is not one site but several. First you have the other non-profit competitors that compete in various niches:
- Stanford Encyclopedia of Philosophy - Supported by Stanford University and various foundations. Excellent articles written by experts on philosophical topics, but suffers from spotty coverage.
- Internet Encyclopedia of Philosophy - Supported by the University of Tennessee. Good coverage. Expert written, pitched at a slightly more accessible level than the SEP.
- Encyclopedia Virginia - Supported by the State of Virginia. Mostly historical articles which are of uniformly excellent quality and written by experts.
- Australian Dictionary of Biography - Published conventionally but available online through the support of the Australian Research Council. Professionally written and almost always superior to Wikipedia.
- Holocaust Encyclopedia - Expert written and available in many languages, though the articles are generally short. Funded by the US Holocaust Memorial Museum.
- Encyclopedia of Earth - Supported by a variety of nonprofits. Expert-written coverage of scientific topics, particularly those related to the environment
- Encyclopedia of Alabama - Funded by Auburn University and the State of Alabama. Expert written and excellent, basically like the Encyclopedia Virginia only for Alabama.
- Similar projects for Georgia and Oregon
- Encyclopedia of Ukraine - Supported by the Canadian Institute of Iranian Studies and private donations. Expert written.
These are just a sampling of the non-profit offerings. What they all share is that they are freely accessible and written by experts. All of them are also primarily supported by organizations and individuals with expertise in the specific area of focus. They are all excellent, but limited to small subject areas.
Commercially, there are also several competitors to Wikipedia. Most obviously, Answers.com, which draws together hundreds of commercial encyclopedias and lets you search them all, as well as WIkipedia and dictionaries. I hate the way answers.com presents its content, but they probably have the largest database of commercial encyclopedia content on the web available for free, and much of it is excellent.
If anyone really wants to put together a Wikipedia killer, the way to do it is to do roughly what Answers.com does, only for the many non-profit encyclopedias, examples of which I presented above. All of these projects have excellent content and completely compatibly goals - making their content available to a wide audience, but they don't have much pull on Google. Someone with the right skills could probably find a way to pull them all together under some broad umbrella.
At the very least, it would be incredibly useful if someone created a portal that allowed you to search the universe of high-quality open-access encyclopedias all at once from a single page. If I had any idea how to do anything with websites, I'd make something like that myself.