NVC is an alternative to GHDL, written in C. It seems to be way ahead of GHDL though: it has nearly full VHDL-2019 support and preliminary Verilog/SV support, while GHDL is still lagging on full VHDL-2008 support.

It also supports the VHPI interface required to use cocotb.

It's interesting to see that open source mixed language simulators are becoming a thing!

Huge fan of nvc, can't recommend it highly enough! It is fast, has excellent language support and issue response on github is amazingly fast even though this is a hobby project. We're using it every day at work.