Windows only: Chrometa, a time-tracking software intended for students and professionals wanting to know where every last minute ran off to, can now be had for free in its desktop version. It's worth checking out, especially for hourly billing.
Chrometa previously offered free licences to students and a select few others, depending on how many they'd sold, and they're now rolling out a web-based platform with a monthly pricing scheme. In the meantime, they've let Lifehacker know that anyone heading to the Pricing link below and entering their information can get a licence for their desktop-only software, previously $US99, for free.
Chrometa is a free download for Windows systems. The one bummer is that it requires a Java runtime to use, but if that's not too far to reach, it's a comprehensive time-tracking tool, for free.