Olivier Poncet is the author of an Amstrad CPC emulator : Xcpc v0.53 for Linux, BSD and Unix. It doesn't emulate the Plus and GX4000 though.

This v0.53 version v0.53 bings a new OpenGL engine with CRT emulation, support of ZIPped .DSK images, AppImage, better PSG and FDC compatibility and minor corrections/ameliorations.

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.