Starting by Clang and GCC, I bet that for most relevant C projects there is somehow an equivalent written in C++, or even more than one, with the exception of UNIX kernel clones.

Let's start with CPython. What is an equivalent written in C++? (Note: there is an equivalent written in both Java and C#. But not C++.)

I guess Numba might quality.

Then we have Pyston, and the ill fated unladen-swallow.