The MintySynth kit - 2.0 is a great way to make your next musical creation while experimenting with electronics and programming.  Open source and hackable, the MintySynth is an Arduino-compatible synth kit that fits in an Altoids tin.

This comes as an unassembled kit so some soldering is required - but the assembly itself is fairly straightforward and the software comes preloaded so creating your next project should be a breeze!  The included software is a 4 voice, 16 step wavetable sequencer that let's you play around with different intruments while controlling the tempo, swing, keys and scale.  You can save up to four 16 note songs, relooping them over and over or reload each individually.  If you do want to program the Synth yourself, you'll need an FTDI Cable since there's no onboard USB.

There's a bunch of examples over at the mintysynth site.  While this kit doesn't come with an altoids tin, we sell altoid-sized tins here!