[joefigura]

Not sure about other chat apps, but to connect to imessage they were originally using jailbroken iphones and now use MacOS virtual machines, according to another commentator. So there is a bit of additional work that would be necessary to fully replicate it.

[jeroenhd]

Looks like you're right: https://docs.mau.fi/bridges/go/imessage/index.html

Disappointing, but iMessage has always been Apple's special little protocol nobody else can use.

Still, there are Docker images out there (that break the TOS) for running macOS inside QEMU, I'm sure someone can script one of those to set up a bridge more easily?