AntiRSI

Mac OS X only: Freeware program AntiRSI is designed to help you avoid repetitive strain/stress injury at your computer.

AntiRSI schedules inobtrusive 13 second pauses every four minutes (if you don't take your hands off the keyboard for the full pause, it restarts the timer). Likewise, breaks happen every 50 minutes, and last for 8 minutes (again, you have to stop typing for it to count). Lastly, you can adjust the pause and break intervals, as well as the pause and break times to whatever you want.
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