Time Tracking system backed by Google Calendar
Timav ("chronology" in Volapük) is a tool for analysing time tracking data collected in Google Calendar.
It evolved organically to fit the work I do, and how I do it, and should probably be used as reference to building your own system.
You can find more details in this blog post: time tracking.
Code is open sourced: https://github.com/szymonkaliski/Timav.