I made this little Nintendo DS sized computer using a Raspberry Pi and a bunch of off-the-shelf parts. It is a fully functional linux computer that can do most things a full system can (games, web stuff, videos, music etc).
You can also output the video to an external monitor, transforming it into a desktop-ish computer.
I make other stuff like this on my youtube channel.
Estimated Cost ~$120
FEATURES:
- Raspberry Pi 2 (900MHz CPU, 1GB RAM)
- 3x USB ports
- 1x Ethernet
- Fully QWERTY keyboard
- backlit 3.5inch Touchscreen
- 1000mAh battery Clamshell case (made from 2x hard drive enclosures)
- Full Linux OS (Raspbian, using i3 window manager)
- Audio/Video out