Remind! is a versatile intuitive tray-based application. It allows to create and schedule reminders than can pop up messages with optional sound effects; start applications or open documents; and shut down, reboot, log off, or power down your system. A reminder can also check for new email, dial phone numbers, display startup messages, synchronize system time via the Internet, send messages, and open a specified Web address. In addition, you can display a stay-on-top Clock, as well as have the program chime or speak the hour, half hour, and quarter hour.
Software that can be used as an alternative to Remind!: