Krakli Synths has released RGB4, a freeware software synth for Windows.

RGB4 features

• Two main sound sources: a 32 partial additive Osc and a more conventional multi-wave VA Osc.
• Individual levels of each partial can be controlled by red sliders at the top left of the display, or by the ADSR sliders ranked below each partial. Blue sliders vary the amount of ADSR modulation and the Green Oscilloscope trace shows the realtime modulation of the waveform.
• Multiwave Oscillator with simple controls and a mix knob to vary the amount it comes into the sound (waveform is indicated by the Yellow Oscilloscope display).
• Global ADSR which affects the overall amplitude of the sound.
• Octave Velocity and Volume amounts.
• Controls for bend range, vibrato, delay rate and amount.
• Filter modulation section with x-y pad.
• 6 filter frequency, resonance, envelope modulation and LFO (with various waveforms) controls.
• Global control for filter LFO rate, including random LFO waveform.
• Phase shift for LFO waveforms.

RGB4 is available as a free download.