ZEsarUX is open-source and multiplatform, having off-the-shelf installers for Windows, macOS, Linux, Raspberry PI, and many others.
The well-regarded ZEsarUX emulator reached version 9.0 bringing a foot-long list of new features and improvements, notably the addition to non-Sinclair machines like MSX, Colecovision, Spectravideo, and SEGA SG-1000.