The CM0 is a Pi Zero 2 W, except in stamp form, with castellated edges, so it's easier to pick and place and solder to another PCB.

It's only being sold in China currently, for integration into OEM products.

Performance is practically identical to the Pi Zero 2 W, though I tested it anyway (see https://sbc-reviews.jeffgeerling.com).

It's a Compute Module, but eschews the more fragile Hirose board to board connectors in favor of castellated edges, for easier assembly.