Raspberry Pi - What can you do with it?
Its named as "An ARM GNU/Linux box for $25. Take a byte!". Its an ultra-low-cost credit card size computer with all the ports you can imagine from USB, Wifi to HDMI.
You can use this circuit to create custom computers or custom hardware like Robots. At 35$ (newer model B) this is a great help in learning computer and easier to program.
Here is an introduction video: