Cesium compiles standard C source code to a .NET assembly. No unmanaged/mixed mode (a-lá C++/CLI) code is generated; everything is fully managed (but may be unsafe). C programs are very useful in the modern world, and solve practical tasks. At the same time, deploying C code alongside .NET code may be tricky (especially if your application supports multiple platforms). Cesium is designed to resolve the problems of C code deployment, and lift it to the managed state (so it is cross-platform in the same way the underlying CIL code it is compiled to).
You won't be able to use Cesium for anything useful today (16 Jan 2022).
Last modified 06 April 2022