http://hellojarvis.io/ is a Messenger bot that reminds you to do stuff. You can phrase time in many ways, which was quite tricky to do: "in 3 hours", "on the 25th", "tomorrow night", "next wednesday" all work.

We currently have almost 25k users and I'm proud of the fact that people really do find it useful. A friend recently mentioned to me that he used Jarvis to remind him about his dentist appointment.