ProcrastiTracker

ProcrastriTracker is an open-source time-tracking tool that automatically tracks which apps and documents you use and lets you view detailed statistics about your usage. It is designed to be lightweight and unobtrusive. It is useful for:

The main tree structure displays all items sorted by frequency of use, including total time, with sub-items listed below. The top level consists of application names (based on their .exe files), and below them is a hierarchical tree based on the name of the window that was active at that moment (the effectiveness of this solution depends on the specific application). Web browsers (supported: Chrome, Firefox, IE, and Opera) also have the domain name of the active page as a second level in the hierarchy, so you get statistics grouped by websites.

The background of the tree structure consists of a bar chart in which the colors correspond to the various tags assigned to a given item (if multiple different tags are used for sub-items, the bar is split accordingly).