Desktop Alarm Clock is a small and fast standalone application. It does not require any registration for download, decompression or installation. Just download it and run it. It takes around 0% of the processor time (you can check it with Ctrl+Alt+Del in your Task Manager) and almost nothing from your system memory. You can set the alarm and hide it in the system tray to free the screen space as well. It will pop up automatically when the alarm goes on.