I too am developing an automatic time tracking application (for the Linux desktop, but I think it might be made to work cross-platform): the idea is that, you just install it, you might then optionally choose apps or files to identify your project activities, and it will auto-detect time spent within those apps; it will come with a pre-populated database of known apps so that it can handle most common activities automatically.

It works by monitoring current processes, and checking the title of the currently focused window, applying a number of regexes to identify an activity, and saving results to a database. It should be able to handle screen savers, visited URLs, and automatically take snapshots of unidentified windows so that you can later map them to a known activity.

I envisioned this tool for personal use; however, it could be deployed to monitor employees in a centralized manner, though this might even be illegal in many countries.