1. A WordPress Multisite (3.5) installation (note: must be Multisite)
2. A XenForo (1.3) installation
3. A MediaWiki (1.20.2) installation
Provide central management via whichever software works best--either WordPress or XenForo. Sign into one site, signs into all. Sign out of one site, signs out of all.
This is a big job. I'll accept offers at email@example.com. I'll also be posting this on WordPress Jobs.