Analogue Synthesizers you could build. Modular and Stand alone boxes. Simple schematics for the modules. The electronic analog basics to build your own synth.
Analog Four synthesizer by Elektron
"In 1997 a handful of students, who got together during a university course at the Chalmers University of Technology in Gothenburg, made a rough prototype of a synthesizer."
"Elektron is an electronic musical instrument company, based in Gothenburg, Sweden, founded in 1998. Its products include the SID-based SidStation, the Machinedrum percussion synthesizer, the Monomachine synthesizer, the Octatrack performance sampler, and the Analog Four synthesizer."
Analog oscillators, Opamp Filters, Ramps. Waveform Generators and Modulators. Generate Square, Sine, Sawtooth/Triangle waves with modulation and mixing.
Music From Outer Space
If you're into electronics, can solder and trouble-shoot, they have many cool analog synthesizer projects.
SDIY aka Synthesizer Do It Yourself
"When I was a teenager, back in the seventies I became fascinated by those weird sounding machines with those huge panels full of blinking light bulbs and knobs."
Analog Synthesizer Resources
"Many of these links are from the "Synth DIY" crowd, a community of electronic music enthusiasts who have collected together on the internet to share electronic design ideas and build synthesizer modules."
Synthesizer Electronic Circuits - Discover Circuits
Hartley Oscillator, produce clean analog signals, paradoxical sounds, simple version of the DDS synth, Precision Frequency generator, Metronome, Beat Box, Tone Generators.