Key Manager is designed to allow distribution and management of SSH keys in a way that scales beyond manually copying public keys to remote hosts. This approaches Single-Sign-On functionality, if limited to ssh access from a single host.
PyUserCreate is a tool for *NIX OSes that allows you to accept user account requests from a web interface, and use a simple command-line tool to approve/disprove requests.
XSDB XML is to DATA as HTML is to DOCUMENT. Publish and combine data as easily as HTML format and web browsers publish and view documents. Implementations in Python, javascript, java, C#/.NET.