Mac: Chrono Slider is essentially an alarm clock with what, at first, seems like one of the most bizarre interfaces you'll ever come across. Once you get to know it, however, it turns out to be a really fast way of adding alarms and reminders that can even control aspects of your computer when they go off.
How Chrono Slider Works
As you can see in the screenshot above, activating Chrono Slider breaks your screen into various segments. Click up at the top will cancel out. Clicking in the middle will set an alarm that goes off after a specific amount of time passes from the current time. The farther you mouse is to the left, the shorter that period will be. Moving to the right will elongate it, letting you set a range anywhere from one second to 24 hours. Heading down to the bottom of the screen will let you set an alarm for a specific time of day. Once you've clicked and chosen your time, you'll slide from left to right to select a preset alarm label. It'll be white if you're just going to see a message displayed, and it'll be blue if it runs an AppleScript (e.g. pauses or plays iTunes, or puts the computer to sleep). You're not limited to the preset options, of course. You can go into Chrono Slider's preferences to edit them. Once you've found the one you want, just click and the alarm is set.
The Bottom Line
This may seem like an in-depth process because of this long description, but once you know how it works you can set an alarm in a matter of seconds. Chrono Slider is actually a really clever app and definitely worth a look.