One of the things I miss about Objective C is just how easy it is to call into a C API, or otherwise include a C function if that's the easiest way to call into a C API.

I shipped a cross-platform C# project, and once I realized I could expose "ordinary C" from the Objective C part, it was very easy to integrate the two without using a framework. (It helped that the UI was 100% Objective C, so there wasn't much surface area between the C# and Objective C parts. We initially used MonobjC, but first I had to work around a shortcoming, and then we needed to remove MonobjC due to licensing and some of the newer C# integration layers were not available.)