A crop of disturbing Facebook apps turned up early last year, alerting its user to a target’s profile change if they signed up with the service. Breakup Notifier sends users a notification whenever a friend they were interested in changes their relationship status to single. Sure, you have to be friends with the person you're interested in before you can even avail of the service, but the thought of someone being able to pounce on you as soon as you're available is more than just a little disconcerting.
Also by the maker of Breakup Notifier, Crush Notifier is a Facebook app that allows you to choose people you are crushing on, and the service sends them an anonymous notification email. If the feeling is mutual, you get a similar email notifying you of your match. But wouldn't it be more ideal to simply man up and be direct with your feelings instead of using such a service?
WaitingRoom lets you anonymously enter a friend's name within the service to give them a hint that they have options. There's a waiting period of two days after the target’s break-up -- because this app is different, it's tasteful -- after which the application discloses the identities of his/her admirers.