A group admin can create a group wiki and corresponding group wiki pages. Each page has settings (which can override the group privacy settings) to control access to the page both in terms of view access and edit access. The group also has a shared document library for uploading files. Page revisions are fully supported, as are revision compares and restores. Activity stream updates for wiki edits are also created, based on an excerpt of the changed text.
The wiki pages are edited with tinymce for lots of wysiwyg loveliness. We chose not to implement any kind of edit-lock, but users are warned if other people are editing the page at the same time. They also receive a more noticable alert should someone else save a page whilst they are editing it. Finally, after 30 minutes of viewing the wiki edit page, the page is automatically saved and the user is returned to the view screen (given a warning 5 minutes beforehand).
Author homepage: http://namoo.co.uk/