Keep control of computer usage
https://bugs.launchpad.net/timekpr

This program will track and control the computer usage of  
 your user accounts. You can limit their daily usage based  
 on a timed access duration and configure periods of day  
 when they can or cannot log in.  
  
 Any bugs should be reported to our bug tracker:  
 https://bugs.launchpad.net/timekpr/+bugs  
  
Authors:  
--------  
Even Nedberg <code@nedberg.net>  
Savvas Radevic <vicedar@gmail.com>  
Nicolas Laurance <nlaurance@zindep.com>