It actually is self hostable (that's how quite a few of our customers use it), but no, it's not OSS (because we needed to build a sustainable business).

Anvil isn't for distributable desktop apps (that's not where most of the action is these days, for better or worse). But we use it for one-offs (driving local code via the Uplink) all the time.

from their perspective, to charge people, I guess