Olivier Poncet is the author of an Amstrad CPC emulator : Xcpc for Linux, BSD and Unix. It doesn't emulate the + models though.

And also quite interesting, he has released in 2024 AYM JS which is a sound chip emulator written in JavaScript emulating the AY-3-8910 PSG (Programmable Sound Generator) and the YM2149 SSG (Software-Controlled Sound Generator). You can test AYM JS here (press the Power button and the Play button). At the moment YM files must be converted to javascript (but the conversion tool isn't available yet), but direct support of YM files is on the way.