Update: The ProofAssistants Private Beta has started.
Stack Exchange will soon (February 8th) start Private Beta site for Proof Assistants and Automatic Theorem Provers. If you want to see what a StackExchange site is like in its initial beginnings, want to help shape the future of that site, or just want the silver beta badge, then I highly recommend getting involved in the Private Beta!
To receive updates about when the site goes live, and when it graduates, and for the opportunity to get rewarded for your early efforts with the site, you can go here, click "sign up" or "login" to make sure your Stack Exchange account is connected, the click "commit".
Often people hesitate to click "commit" because it asks you to promise that you'll post at least 10 questions or answers on the new site, but don't worry about that because most people that click "commit" do not fulfill that commitment, and there's no negative consequences for not committing. However if you do follow through with your commitment you do get rewarded for that.