Great question. Here are some candidates:

* https://github.com/rswier/c4

* https://github.com/Fedjmike/mini-c

* https://github.com/rui314/8cc

* https://github.com/rui314/chibicc

* https://github.com/aligrudi/neatcc

Some of them are actually interpreters, and I personally would be interested in actual compilers that generate machine code.