I use it pretty heavily on C++ stuff at GitHub.com/sourcemeta. i.e. take https://github.com/sourcemeta/blaze and this example recent run: https://github.com/sourcemeta/blaze/actions/runs/25751796502.

12 jobs per PR for up to 30 minutes running Linux, macOS, and Windows jobs on LLVM, GCC, and MSVC in static and shared builds with also some sanitiser configurations.

And consider across projects we might send dozens of PRs per week.

Right now it's somehow all fully free on GitHub Actions. I wonder what the same would cost on i.e. CircleCI