Chifir Engine was my second game engine project. I wrote it without using the C runtime or C++ STL and very few outside libraries. I never really reached the point of it being anything close to an engine, but I designed and partly implemented an RHI, and a basic SIMD math library.

After a certain point it was more of an exercise in writing support code and platform glue than an engine, but I learned a lot from it. I gained a much better understanding of abstraction and SIMD from it.