If you look around the OS X app store, you won't have much trouble finding any number of productivity management apps based on popular techniques like Pomodoro. We're big fans of these utilities here at TUAW. They transform your work into short manageable chunks, enabling you to return to work with renewed vigor and focus.
What caught our eye with Rest (US$4.99) was its coached breaks. Rest doesn't just tell you when to take a mental pause, it helps coordinate a short physical refresher with the cognitive one. That's a really clever twist for a crowd that might be a bit tomato-weary.
There currently just over a dozen different breaks in all, but that is plenty to for a normal workday. Perhaps the developer will offer more options in the future as app upgrades for greater variety over time. The breaks on offer are easy to do at your desktop and don't involve any special equipment.
The app is easy to use. It sits in your menu bar and you can adjust how long each work period and rest period should be. The audio tones were pleasant. The exercises were easy to follow. If you like this category of apps, Rest will easily fit into your work style.
An upcoming iOS companion app promises to offer break reminders when you step away from your desk.