Wikispaces - an online space for groupwork for ordinary people.

Wikispaces is a place for people to easily build web pages together. Anyone can join the site for free, create a space, and begin contributing within a matter of minutes.
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We're firm believers that wikis can be revolutionary tools for building communities. But most wikis are very engineer-focused: hard to use, buried under busy user interfaces, full of features only a geek could love. Wikispaces is our attempt to build a wiki that's easy to use and easy to adopt for all kinds of audiences. We've kept the tool simple so that you can focus on building content, talking with other members, and growing your community.

I wonder whether wikis can (will) be as widely adopted as blogs.