Developer website: www.kimai.de
Its simplicity is its strength. Due to Kimai's Web browser based interface it runs cross-platform. Also it runs cross-network. Likewise you can install it as a Web service or as a single-user program on your local workstation.
While there are many programs one can use for time and project tracking, they tend to be overkill for my rather simple needs. Kimai came about because I was tired to feed lame boring excel tables.
Kimai does not have to run to do the recording. Even with a recording running you can quit your Browser. Your time is still recording until you stop it from any Web browser that has access to your installment. It is designed to hold lots of users but you can use it for a single user if you need to.