Mac: We've discussed how important it is to get up from the computer, but most apps that remind you so irritating we eventually disabled them. Awareness takes a more muted and subtle approach when telling you how long you've worked without a break.
Awareness uses the sound of a Tibetan singing bowl to tell you that it's time for a break. The chime is assertive, but still gentle. If you ignore it, the app doesn't nag you, it just waits for the next hour where the bowl will chime twice to tell you it's been two hours, three for three hours, and so on. Awareness is $2.49 in the Mac App Store.