GNOME Break Timer
Break Timer keeps track of how much you are using the computer, and it reminds you to take regular breaks. It is designed to encourage healthy behaviour, with a mix of short breaks for your eyes and wrists, as well as longer breaks to keep your body moving and your mind on task.
Break Timer is simple to set up, so you can pick a break schedule that works for you and it will carry on working in the background.
This application is intended as a new alternative to drwright, which was included with GNOME 2. GNOME Break Timer is aimed squarely at GNOME 3, with a status application that follows the new design patterns as well as tight integration with GNOME Shell. Right now we use xlib with the xrecord extension to monitor activity, while the rest of the application is straight-forward Vala code with GTK+ 3.
Ubuntu (daily builds): https://launchpad.net/~brainbreak/+archive/experimental
Source code (git): https://git.gnome.org/browse/gnome-break-timer/
Bugs on Launchpad: https://bugs.launchpad.net/brainbreak