The command used for this can be invoked on any OS that Now CLI supports (Linux, Alpine, macOS and Windows). In terms of the languages that are supported, there's no end, really:

https://github.com/zeit/now-builders/tree/master/packages

(These are just the default ones, you can add your own language using https://zeit.co/docs/v2/deployments/builders/developer-guide...)

(I know Nix, not so much Now.)

Given what I read in this thread and their docs, it looks like they are still searching for a coherent solution to solve the "deploy my app" problem (from Docker with v1 to AWS lambda in v2), and they appear to be very vendor-specific with solving it.

The main goal seems to be to condense any action a developer might want to do into a single command.

It pretty much seems geared towards the JavaScript ecosystem.