I'm not really satisfied with Appveyor and Travis. The builds are pretty slow, so I'm considering switching to Circle CI or Azure Pipelines or something. There are a bunch of options in this discussion.

It might be best to just leave the macOS builds on Travis and switch Linux and Windows to something else, but I also don't really like having to maintain so many different types of CI.

Cirrus CI (which is what we now use for FreeBSD) support 8 Linux, 2 Windows, 2 FreeBSD, and 1 macOS build at the same time, so we could also just switch to that and call it a day. I feel like it will still be too slow though for the Windows and macOS builds at least.