Do you know some free alternatives to Google Wave to collaborate with other people on discussions/projects. They should provide at minimum the following features:
- Create private discussions
- Invite people to discussions
- Possibility to edit other users posts
- Simple text formatting (bold, italic, colored font)
- Track changes since last visit
Additional nice and welcome features are:
- Insert polls
- Share documents (editing capabilities would be great)
- Share images
- Share attachments
UPDATE BOUNTY: Now that Google has announced to abandon Google Wave project, I really need an alternative.
UPDATE FREE: Free means that spend money on hosting a script/software is not a solution for me.
UPDATE REQS: I removed sharing of images/attachments/documents from minimum requirements.