
pbwiki
Creates wikis which are easy-to-edit web pages that let you collaborate online and share information. This free version comes with unlimited pages and revisions, 10 megabytes of storage for file attachments, zip backup and RSS feeds.
When you want a group of people to collaborate on editing text.
If you are posting completed text rather than editing.
Easy to get a group of people to collaborate on editing a document. Does 'versioning' so you can easily go back to a version prior to changes.
Free accounts mean you have to put up with advertising.
Organisations which need to gather a large number of information for their campaigns can ask their supporters to do the research and add it to a wiki. A wiki can also be used to collect a list of best practices in the activism world.
Pbwiki, Inc., http://pbwiki.com/about.html
They say 'Your stuff is yours; we don't own it when you post it. We don't police you, but if the police tell us to take your stuff down, we will'.
Your wiki will be password-protected so that only people you invite to edit the wiki can do so.