You mentioned that you started working on the login/signup/mailing list app. I put some thoughts on a diagram:
This is how typical registration for an application with a server side component could work. What are your thoughts?
The idea is that this process will set a SSO cookie that will allow users to automatically be logged in on http://discourse.p2pu.org and http://community.p2pu.org (and potentially on any other *.p2pu.org domain).
I haven’t thought through the flow for an app without a server side component yet.