Qaop is described as 'QAOP lets you play ZX Spectrum games right through your browser. Choose from a large selection of classic games or select 'Open' from the emulator's menu system to load a game from your computer' and is an website in the Gaming Software category. There are five alternatives to Qaop, not only websites but also apps for a variety of platforms, including Windows, Linux, Mac and Android. The best alternative is Fuse, which is both free and Open Source. Other great sites and apps similar to Qaop are Retro Virtual Machine (Free), Speccy emulator (Free), JSSpeccy (Free, Open Source) 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.
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.