Udacity is a web-based college/university that offers free courses in various computer-related subjects. Courses typically last 7 weeks, and you can follow at your own pace in your own time. At the end of the course there's an exam, so that you can be awarded a grade.
The courses are free to access, and cover a variety of topics, with more due to be added soon.
Check out www.udacity.com to find out more.