StackCompare is a tool that lets you see how you're doing on StackExchange sites relative to other people, be they friends, rivals, or some combination. Track your and their reputation over time. Compare badges held. Watch as you overtake them in the ranking list.
StackCompare is currently closed-source, but the app is free-to-use, with no plans to change this.
StackCompare should work on all modern major browsers; it was developed in Google Chrome, and while it doesn't look great with Lynx, it should still be usable.
StackCompare was written in Python using Django, TempoDB to store historical reputation, Neo4j as a storage backend, Twitter Bootstrap for the UI, stackpy for interfacing with StackExchange, and hosted on Heroku