I'm looking to create a site that allows registered users to create their own groups and have their own group blogs. They should be able to have a group page with a few details about the group and it should show the group blog. I've thought of a couple of ways of doing this but both seem to require custom plugins.
1) Use the BuddyPress plugin. This gives the groups but there currently is no BP plugin that allows group blogs.
2) Use categories. This gives the group blog if categories are set with permissions as to who can post using them and if each blog post can only have one category. Would need to create a plugin that allows users to create a new category and have that as the 'group'. The plugin would also need to allow group members to be invited.
Is there another way to achieve this is WordPress? Any help would be greatly appreciated.
Note: I don't want to use WordPress MU.