I keep saying the best free synths are the ones that steal a trick from hardware, and this one stole a whole rack module. Push and Groove's MICRONIX takes the original open-source DSP from Mutable Instruments' Plaits, which is basically the most beloved macro-oscillator in all of Eurorack, and puts all 24 of its synthesis models into a free VST3/AU.
So you get the full Plaits spread: virtual analog, FM, wavetables, granular, physical modeling, and the percussion models, each with the same three macro knobs (Harmonics, Timbre, Morph) that change behavior depending on the model. It also keeps the authentic low-pass gate mode, which is the part that got me. Run the percussion and physical models through that LPG and you are in struck-metal, clangs, and thumps territory. Exactly the stuff I reach for when a track needs to sound like it was recorded inside a factory.
It is monophonic with retrigger and legato modes plus glide, so this is a bass, lead, and percussion weapon, not a pad machine. The four-row mod matrix covers velocity, mod wheel, aftertouch, and key track with bipolar amounts, and the LFO has five waveforms with DAW sync. There's also an on-screen keyboard with a Hold button and a Randomize button, which is a dangerous combination when you have 24 oscillator models to burn through.
The GUI is resizable with a live waveform display, and it ships as 64-bit VST3 on Windows and universal AU/VST3 on Mac.
Price: FREE. If you want more, MICRONIX PRO ($19 intro, regular $29) adds dual engines and polyphony.
Grab it at pushandgroove.com/micronix, from Push and Groove (pushandgroove.com).