Meetcha At is an app for iPhone and Android which lets people make plans to meet up with their real friends in the real world without all of the usual hassles.
With Meetcha At, you simply create 2 polls, one for time and one for place. Then you send it to all of the people you want to meet, and let them vote. It is very simple for both the person doing the inviting, and the people being invited. Everyone votes anonymously and the app determines the winner.