You can take a look at Pinta[0] I don't recall if it's a clone or a port of Paint.Net, but works for me as a quick tool... the OS integration (open with) needs some work though. It uses Mono as a portable runtime and is decent enough, again for most work. IMHO easier to use than Gimp, though not as feature rich.
https://pinta-project.com/pintaproject/pinta/