Khorlo is a free physical-modeling synth from Aaron Jasinski, released under the name JAS-I. Instead of oscillators, it uses a spinning virtual cylinder ringed with eight physically modeled strings, struck by eight independent pluckers whose speed and position generate emergent polyrhythms. Bowed resonators add a sustained, singing alternative to the plucked attack.
Deep modulation keeps it from being a one-trick tool: eight modulator banks, six of them graph-based envelopes or LFOs, plus four macros, velocity, mod wheel, aftertouch, and MPE, routable to nearly any parameter. Nine filter models and a ten-slot reorderable effects rack finish the sound. Formats are VST3, AU, and CLAP on macOS, Windows, and Linux, and it is currently in beta at version 0.9.03.
Use Chromaphone 3 when you want a mature, stable acoustic-modeling synth with a large preset library, listed at $199 on that card. Use Serum 2 when the work is wavetable design rather than physical modeling. The full breakdown is the Khorlo feature review.