Work time stress relief

After weeks of neck pain, I went to the physiotherapist on Saturday and she's loosened some vertebrae (3-4) which were very stiff, and thinks with improved posture, 7,8,9 will become looser naturally.

She's advised I get a lumbar support to use on my office chair and at home when sitting on the sofa, as well as to raise my monitors on the desk. The former is ordered, the latter is done (though they're still not quite high enough.)

The final part I need to do are exercises with my neck every few hours. I could set an alarm on my phone, but I don't want it going *beep* *beep* *beep* and annoying others. I'd prefer some sort of popup mechanism on the computer.

I run Linux at work – Fedora 14 (don't laugh, not my choice) – what is the recommended 'take a break, do some stretching' alert software? Something which just pops up on the screen, no noise, click to dismiss. Any suggestions?