[karmakaze]

I would suggest perhaps a language/framework that compiles to a single binary. I'm assuming that the back-end doesn't need to do any heavy lifting. You could use Go, Crystal/Kemal, Nim/Jester or other combination.

Do you actually need the same deployed code to run on each platform (Net/Java) or is it sufficient to have common source that produces a binary for each?

[darreld]

That is a great point. I don't think I actually need the same deployed code to run everywhere. Common source would work. I do, however, feel like I need a language that is capable of producing an app that can be managed by a user, such as a UI for starting the backend process (UI or Windows service).