YoYouWantTo was initially founded at the Wharton School, and has received awards and seed funding.
The idea is fun! It’s a simple way to get people to do spontaneous activities with you offline. It hasn’t been launched yet, but can be previewed at www.yoyouwantto.com.
Contact Nik at nikhilan@wharton.upenn.edu if you know Rails and are interested in helping out!