ChallengeBot is a tool that combines a bunch of my adhoc scripts and tools from the last few years I've used for managing and sending out coding challenges. It handles invites, scheduling, time limits, Git repository hosting and progress tracking.
It's made my life a whole lot easier, so I figured others may be interested as well. And you can try it without having to sign up for an account!
How does the time limit system work?
When a candidate starts the challenge, a unique Git repository is automatically created. Once the timer runs out (configurable per-challenge), the repository goes into read-only mode and new pushes will be rejected. It'll also upload the contents of the repository and email the admin with a download link to the zip file.