synth.ist is a free modular synthesizer that runs entirely in your browser — no account, no install, no plugins. You patch nodes together with cables on an infinite canvas: oscillators, wavetables, noise, microphones, sample pads, and audio and video players as sources; filters, delay, reverb, distortion, compression and parametric EQ to shape them; LFOs, envelopes and control voltage to modulate anything you can point at.
What you build can be measured as well as heard, on an oscilloscope, spectrum analyzer, spectrogram, tuner or loudness meter. It reads microtonal scales from Scala .scl files, learns MIDI on any parameter, bounces offline to WAV, and keeps a persistent sound bank of your own patches and samples. It installs as a progressive web app and works with no connection at all — nothing you make is ever uploaded, because there is no server to upload it to.