Wikipedia wasn't really "new". Wikis have been around before. There were a dozen of encyclopedia attempts around (although maybe not using a wiki, and usually more focussed around a specific field of knowledge), there were huge collaboration applications.

I think that Wikipedia just offered the right options for the users at the very right moment, when this "revolution" - people not using the web as a way to 'download' content as much, but to actually publish their very own stuff, taking over content production - was just kicking off, without being too fragmented yet.

Today, you'll find dozen of "encyclopedias" for specific parts, who somewhat try to copy the success of Wikipedia, but which maybe was so successful because it didn't put up much restrictions on what it was to be used for...

As for the "not new" part - take for example a look at DMOZ.org, which is for example used by Google as datasource for Directory.google.com. This has been around for years (since 1995?), 5 Million verified Links in there, 70k editors just to verify and organize the links (many just taking care of a small part like the links for their home town), and everybody can submit new links. I started being an editor when it had around 2 Million links, and "timed out" due to inactivity when it reached 3 Million.

I have the impression (partially of course to the success of search robots like google, who have also "ruined" the directory business for e.g. Yahoo) that growth slowed down horribly the last years a lot. Although the level you could contribute wasn't that different from what e.g. Wikipedia offers.

On the one hand it's a shame that great projects like DMOZ get so little attention, but on the other hand e.g. Wikipedia is fantastic, and I'm happy that many people have realized that they can be an active part of the web, not just a content consumer. That there is more to the web than to share music and access pr0n^Wcommercial websites.