I want to create a somewhat simple user database system with invites, user registration, profile generation, and possibly other things down the line, such as PMs, and possibly maybe a forum (BBPress?) someday. I have SQL setup, and could make the PHP myself, but I figured I would look for a really solid template code to work with. For now, I'm trying to keep it simple, so no exceedingly complex CMS is necessary.
Any recommendations for this sort of thing?