Speccy emulator is described as 'Speccy is a cross-platform emulator for Sinclair ZX Spectrum' and is an app in the Gaming Software category. There are five alternatives to Speccy emulator for Windows, Linux, Online / Web-based, Mac and Self-Hosted solutions. The best alternative is Fuse, which is both free and Open Source. Other great apps like Speccy emulator are Retro Virtual Machine (Free), JSSpeccy (Free, Open Source), Qaop (Free) and Spectaculator (Freemium).
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.