I just released rerun 0.7. It now uses the Listen library which uses your OS’s built-in filesystem change monitoring features so CPU use is much more efficient.

Rerun launches your program, then watches the filesystem. If a relevant file changes, then it restarts your program. Rerun works for both long-running processes (e.g. apps) and short-running ones (e.g. tests). It’s basically a no-frills command-line alternative to Guard, Shotgun, Autotest, etc. that doesn’t require config files and works on any command, not just Ruby programs.