Lawn mowing is quite fun task, but it may be much more fun if lawn mower could be controlled remotely. To do so, you need an Arduino, R/C transceiver and couple of electric wheelchair motors.
Arduino takes commands from R/C receiver and according to them controls wheel motors via H-bridge motor driver. Sounds familiar to hobby R/C modeling. Next time you go to mow the lawn, take remote control and scare your neighbors.