With KAlarm you can schedule an alarm message not only by setting a particular time, but alternatively by specifying the amount of time between now and when the alarm is supposed to occur. For example, if you put something on the stove that needs to cook for 20 minutes, you simply set the time interval to 20 minutes. You don't need to first figure out what time it is in 20 minutes and then enter that time as you would when using a calendar program.

KAlarm has many useful options, including:

• choice of text message, image file, command execution, or email
• recurring alarms
• reminders before actual alarms
• choice of beep, sound, or speech

For more information see here. Ubuntu users can install KAlarm using the Add/Remove option under the Applications menu.