UNIX for Advanced & Expert Users

Looking for a recommendation -

I'm looking for a reliable domain control panel (like cPanel) that is open source, and I can customize it do work into my work flow.

Essentially, I need new users to be able to create a new account so that
a) a new subdomain is created, or
b) a full domain is created (with nameservers noted)

The domains could reside on one of several machines, so the panel should ideally be able to load balance out the domains, or allow me to program some logic in to account for removed accounts, high load machines, etc

Any thoughts or recommendations?

Thanks

Matt