Peggy2 is an electronic peg board with a matrix of 25×25 LEDs. Peggy2 was designed by Evil Mad Scientist Laboratories and kits are available on their store site. I built a peggy2 earlier this year and have been tinkering with it.
Peggy2 is Arduino compatible as it’s run by an ATMega168 (or 328p) microcontroller. One of the first projects I worked on was a simple message board program called peggyboard. This program lets you write and save a message using the navigation buttons. The characters are 3×5 pixels each allowing for 6×4 characters on the board. The message is stored in EEPROM so it can be re-displayed when you turn the peggy back on.
Here is the Arduino sketch for Peggyboard. You also need the Peggy2 library installed in order to compile the sketch.