The Nag is a Rails To-Do/Reminder application created by a group of Omaha Code School students (see the contributors here). A user can create a to-do list for several different events and the application, using Twilio, will send them texts to remind them of their uncompleted tasks.
It is a little rough on the edges but an impressive effort since it was the group's first full-stack Rails application with large team collaboration and it was completed in 1 week.