As of 2015, some good free alarm clock programs for Windows computers are WakeupOnStandBy and Free Alarm Clock, while a good free alarm clock for Mac OSX is Wake Up Time. WakeupOnStandBy wakes a computer up from sleep mode and performs user-specified actions, such as playing music upon waking.
Free Alarm Clock lets users set up multiple alarms and use their own MP3 files as alarm sounds. The portable version of this program can run on a flash drive without installation. Wake Up Time supports 24-hour mode and allows users to add custom alarm sounds. The main switch button in this app lets users turn the alarm on and off easily.