I helped with the initial Aarch64 emulation support for qemu as well as working with others to make multi-threaded system emulation a thing. I maintain a number of subsystems but perhaps the biggest impact was implementing the cross compilation support that enabled the TCG testing to be run by anyone including eventually the CI system. This is greatly helped by being a paid gig for the last 12 years.

I've done a fair bit of other stuff over my many decades of using FLOSS including maintain a couple of moderately popular Emacs packages. I've got drive by patches in loads of projects as I like to fix things up as I go.