Chibil: A C compiler targeting .NET IL
github.comThis is a c compiler (chibicc) ported to c#, and updated to emit .net IL ie bytecode.
The CLR model has always had support for instruction to support the C/C++ language, compile plugins or similar once and load/run on multiple platforms should be possible.
However, iirc there might've been some issues with libraries making the cl /clr code unportable (don't quote me on that though), starting from scratch might yield a better result if one just wants to run C code everywhere.
Note that Microsoft "cl /clr" also does this. It's a bit of a niche use case.
The creator of lcc also published a paper "lcc.NET: targeting the .NET Common Intermediate Language from Standard C" (2004).
<https://drh.github.io/documents/msil-spe.pdf>
One problem with lcc has always been that it's distributed as source available with restrictions and has never been available under a FOSS license.
OrangeC targets IL too.