Synth # 2, its a brilliant design from Beavis Audio (the site is currently down but check out the version saved by the wayback machine), a DIY hero, and a great inspiration upon my introduction to the world of electronics.
This synth uses 4 oscillators off of a CMOS chip, running a different ranges to produce different sounds. Each oscillator has a frequency knob, as well as a mix knob, and a switch to go between resistor mixing and diode mixing. To the left of the LED, we have (from bottom to top) a filter to further shape the sound, the power switch, and a voltage starve knob, to glitch up the oscillations real nice. All of this means a ton of options and variety in the sounds coming from this alien. The demo below is the synth by itself, but it sounds great with reverb and delay added.
Beavis also added to this circuit, producing the Heterodyne Peyote Space Explorer. I've built this as well, but am still troubleshooting it. I'll be sure to add a video of that once it's all set. In the meantime, enjoy.