Any open source user management/subscription systems?

A while back I probed around to see if there are any open source user management systems out there and didn't come up with any great leads.

Weird thing, at my day-job, yesterday, the general manager asked me the same question.  Clearly there is a need for something like this.

My original list of requirements went something like this:

• Allowing users to sign up (email verification, catpcha support, configurable list of user details to require)
• Assign various access levels (or attributes?) to users.
• Allow users to log in / log out 
• Detect multiple failed logins for a user or from a source host with configurable temporary lockouts
• Provide a simple API to use in applications that build upon it to get login status & access level (preferably language-agnostic)
• Mechanism for retrieval of forgotten passwords (email? security question(s)?, combination?)
• Provide a simple html based UI to handle all of these functions (including administrative functions like approving, disabling, changing access, etc.).
• Provide an XML-RPC based interface to perform all of the functions so it's easily customizable by application that build upon it.

A new requirement that this request brought up was:

• Support for paid subscriptions
  

So here's another blog post, and I'll go hit up the OSFlash mailing list to see if anything comes up.