Punch-clock is a project mainly written in ..., it's free.
Simple Python tools for tracking your time on multiple projects and generating billing reports; they use a human-readable and editable text file database.
punch-clock
Daniel S. WilkersonThe punch-clock tool tracks your time as you start and stop work on a project. It records its state to a file in your filesystem in a simple, human-readable and editable format.
The punch-clock-report tool will generate a report from this database.
Both tools are released under a BSD-like license which you can see in the comments in the program files.