One of the nicest part of Nit in my opinion is their foreign function interface (FFI). It currently supports C and Java out of the box, and Objective-C and C++ are being worked on. I had the chance to work with the FFI a few years ago when it was still a student's master project, and I really had a blast with it. Some librairies such as libcurl[1], curses[2] and sdl[3] were implemented with this FFI.
Another great part of this language is a project being worked on by the same guy that built the FFI, and it's a cross-compiler for mobile applications called Gammit[4]. You write your app in Nit and compile to Java and Objective-C natively for Android and iOS application. The iOS part isn't ready yet, but the Android one is quite advanced with a few great examples such as a small Minecraft clone working with Google Cardboard and having multiplayer functionality.
[1] https://github.com/privat/nit/tree/master/lib/curl
[2] https://github.com/privat/nit/tree/master/lib/curses