Developing a service app on Kali Linux

I am new to Linux world and is seeking advice from experts

I need to develop a service app (kind of like Windows NT service that auto starts) on Kali Linux, calling some external C libraries.

What would be the best Elements language/platform to do that? Island? .NET core?
Any GUI support?

Thank you.

Check out Writing Linux Dæmons with Elements. Any language will do fine. this article covers native (Island), but .NET Core is also a good option.

RIght now you’re pretty much one your own for that, I’m afraid. Gtk is one (low-level) option.

Thank you

Is it possible to connect from Linux to a Windows RemObject SDK service?

Of course, yes.