Current status: Beta! See the main wiki page for current status and the compatibility list for support status of various DOS programs and other system compatibility notes. This project has a heavy demoscene focus due to the GUS's history so that's what I've concentrated on, but GUS support in games is quickly improving.
Want to make your own beta PicoGUS? See the build guide. Important caveat: due to the specs of the Pico, assumptions made by programs written to use the GUS, the imprecise nature of emulation, and the varying specs of retro DOS PC hardware, some things will likely never be perfect. This is still a work in progress.