Ask HN: Invite-only beta test management platform?

With everyone and their dog creating a web app these days, and with 75% of them running invite-only beta tests, it boggles my mind that no one has released the code for their beta test management system (i.e., collecting and management invites, creating and releasing beta invite codes, etc.).

Yet, I can't find anything.

The closest thing I have been able to find is http://www.prefinery.com/ which is a SaaS app for managing beta tests. Surely there must be others, though? Certainly someone must have put up their beta management code on Github, right? Maybe someone's created a Rails plugin for this? Something?

Or does everyone just roll their own...? To me, there seems to be an opportunity here.