I have downloaded and tried several of these types of applications. The one thing I like about this one, which may seem like a very small issue to most, is that when the alarm is finished, a small window remains on your screen, notifying you that it went off. Should you be away from your computer for some reason, you would return and find this window informing you that it did indeed sound while you were gone. Other applications I own merely sound for a few seconds, and that's it. If you should be sway from your Mac, you have no idea it went off. For this reason, I'm using this one.