The inPulse watch is a great platform to hack on. It has an ARM7, 32 KB of flash and 8 KB of RAM, Bluetooth, a buzzer, an OLED screen and a button. Not much by today’s standards, but plenty to play around with. The programming environment is very much like a microcontroller; no multitasking, no dynamic memory, and very constrained memory/cpu. That is, of course, what makes it so much fun.
Hackable inPulse Watch, Now With a Screen Saver!