>>5
On the server side you have Vapor, it's MIT-licensed and runs on Linux.
https://vapor.codes
But you're right, the whole point is about the Apple ecosystem and the access to the Apple Store where you can sell your shit for money. From my point of view, I couldn't care less about Linux/FLOSS or about anything that involves spending my precious time without financial incentive. I know, the adult life is kind of sad.