Murmur vs Baby Audio Grainferno: the closest comparison
Both are granular instruments with two morphable samples and grains that reach audio rate. One ships a library, the other assumes you bring one.
Murmur vs Output Portal: an instrument and an effect
Portal granulates whatever is on the track; Murmur is a sample you play from the keyboard. Which job you have decides which one you want.
Murmur vs Audio Damage Quanta 2: two granular instruments
A genuine like-for-like. Quanta is the deeper synth, Murmur is built around slicing and playing a recording, and one of them is free to try.
What Murmur's free version does, and what a licence adds
The whole grain engine is free and does not expire. A licence buys modulation, a second layer, the sequencer, the FX rack and saving presets.
The Murmur walkthrough video, transcribed
The full 13-minute Murmur tutorial with a clickable transcript: every control from loading a sample to Morph, timestamped so you can jump.