thingstruments

The Mixtape Alpha is a $42 synth / sequencer smaller than a cassette tape. It is limited to chiptune style sounds, but is still very cool and very portable - you can easily take it anywhere with you. The schematics and source code are available to download, which makes it possible to even build your own.

This guy made a microphone out of a telephone handset and made an instructable out of it . He used quite simple electronics and the sound quality is not very good, as you can hear in the demo video he posted . Anyway, it's a nice idea and gives some use for the old wired telephones. See also this cool video of a studio performance with two DIY headset mics! Erikino & James Studio Perforance