While it wouldn't qualify as a robust alarm clock or reminder application, System Up Time Monitor effectively keeps track of your computer's uptime and throws in some extras.
This app's sliding toolbar-like interface is well-designed and easy to use. The program, which resides on the system tray, monitors the number of days, hours, minutes, and seconds your system has been running. You also can schedule shutdown functions, such as turn off, log off, or restart when your specified uptime is reached. Or you can kick your system into hibernate mode, prompt an alert message, or run a program at a certain time.
If you're looking for the ability to set multiple entries, this application will disappoint. Nonetheless, if you want to see how long your computer's been on and want reminders on when to take a break, System Up Time Monitor is a solid choice.