The Colorspace has released four free synthesizer plug-ins for Windows (VST):

• Feeling is a 3 oscillator Additive Synthesizer with a Saturator for each OSC, 2 Filters, 2 LFOs, Distortion, Double Chorus and 2 Delay effects.
• Drafter is a 3-drawable-oscillator synthesizer with 2 Filters, 4 LFOs, a Bit Reducer, a Stereo Enhancer, Delay and Reverb effects.
• Serio3 is a 3-oscillator Subtractive Synthesizer with 3 Sub OSCs, an ADSR for each OSC, Ring Modulation, 2 Filters, 2 LFOs, a Stereo Enhancer, Delay, Reverb and Chorus Effects.
• Cloud is a 3-Morphing-oscillator synthesizer with a bitcrusher for each OSC, a Filter, 4 LFOs and the Automorph section where you have 4 LFOs to morph waveforms automatically, a Stereo Enhancer, Delay and Reverb effects.

The Colorspace software synthesizers are free downloads from thecolorspace.