We're using OBS for building stuff (and heavily abuse it for the Linux side already) - a few things (like reverse dependency builds) make that more useful that most of the other stuff out there on complex projects. So when the requirement for some Windows builds came along (which are tiny compared to all the other stuff we're doing) we just ended up using WSL to have Windows workers in OBS. Also has some other advantages with how our cmake builds work (short version, developers can do their own bit in visual studio, and then a bit more checks run on CI where we can reuse the usual stuff without caring about Windows)
The Opensuse Build System. It's pretty good at figuring out if something needs rebuilding, so in some cases violating it and making it do stuff it's not supposed to is a sensible choice.
