For several years now I have tracked my effort using org-mode in Emacs, for work and other projects. This has a variety of advantages and disadvantages, but for some time now I have felt a number of its disadvantages keenly. Specifically, it is somewhat painful to check in and out of tasks on multiple computers, and the reporting interface, while powerful, always sends me to the documentation.
I have surveyed the open source time tracking field several times, but never really walked away feeling like there was a tool substantially superior to what I was using. Most tools either required a web browser/server, weren't really targeted toward my use case, or were no less complicated than org-mode clock tables.
Thus et was born. et provides a command-line interface to time tracking and has limited support for distributed operation. It is implemented in ruby and makes some effort to be a good caretaker of your data. Tasks in et form a tree structure, so it can be used to track several different domains as subtrees; e.g., it can track both work and hobby projects independently.
et is far from a finished project, and the initial release version number (0.1.0) reflects this. However, it is far enough along that I am using it as my primary time tracking tool, so it may be useful to others, as well.