MultiTimer, a lightweight application, allows you to track your time commitments to multiple items simultaneously. You type in the timer label, set the inital time and count method (countup or countdown), and the application handles the rest.
In particular, if you need to track (and, optionally, aggregate) time usage for multiple projects, you can assign one timer per project and track your time use per day. Or per week. Or per month. Or per year. Or, if you follow the ABCD life management method, you can assign one timer to each category.
You can download the stand-alone application (15kb) or the installer (200kb).
You can download yTimer from here.