HELM is an open source synth built by Matt Tytel.
HELM includes,
- 32 voice polyphony
- Interactive visual interface
- Powerful modulation system with live visual feedback
- Dual oscillators with cross modulation and up to 15 oscillators each
- Unison and Harmony mode for oscillators
- Oscillator feedback and saturation for waveshaping
- 12 different waveforms
- 7 filter types with keytracking
- 2 monophonic and 1 polyphonic LFO
- Step sequencer
- Lots of modulation sources including polyphonic aftertouch
- Simple arpeggiator
- Effects: Formant filter, stutter, delay
Even more interesting though HELM is a a free software and consequently you can examine and investigate the code online at (github)[https://github.com/mtytel/helm].
More details online.