Fuse (the Free Unix Spectrum Emulator) was originally, and somewhat unsurprisingly, a ZX Spectrum emulator for Unix. However, it has now also been ported to Mac OS X, which may or may not count as a Unix variant depending on your advocacy position.
Speccy is a cross-platform emulator for Sinclair ZX Spectrum. FEATURES - Emulates 16kB, 48kB, and 128kB versions of Sinclair ZX Spectrum, Spectrum +2, +2A, and +3, and Timex Sinclair models. - Supports all types of ZX Spectrum joysticks and the Kempston mouse.