If you've ever asked a friend or coworker to call you at a particular time to help you escape an interminable meeting or end a bad date, you're in luck. 

Enter your own phone number at a simple new site, phonemyphone.com, and choose a date and time. The site will then ring you (for free) at the time you specify. You could also have it call you immediately, which could be useful if you want to find your cell phone and don't have another phone handy, as killerstartups.com points out.

Sounds deviously useful, and when I tried it just now the call came immediately. An automated message said where the call was coming from, and also said I could hit '9' to prevent future calls just in case some miscreant used the site to make a prank call.