Klok (All platforms with Adobe AIR, Free)
Built with Adobe AIR, Klok is a lightweight and cross-platform tracking solution. You can create a hierarchy of projects and sub-projects in the task-management sidebar and then track the time spent on each by dragging and dropping them into the workflow for the day. While you can delve into the details of each block of time, simple adjustments like expanding the amount of time you've worked on a project is as easy as grabbing the edge of the block with your mouse and tugging it down.