ZXSpectr
https://github.com/chernandezba/zxspectr
It's a ZX Spectrum emulator written entirely in Assembler. It runs under MS-DOS, and pretty well also in Windows and MS-DOS emulators, like Dosemu and Dosbox. It's the first emulating the Inves Spectrum + (a Spanish clone)
You can try a newer and better emulator, made also by me, for Unix systems (Linux, Mac, Raspberry Pi and others) and Windows here:
https://github.com/chernandezba/zesarux
Features:
Emulates 16k, 48k, Inves Spectrum +, Spectrum 128k (English and Spanish), Spectrum +2 (English, Spanish and French) and Spectrum +2A (English and Spanish)
MS-DOS, Windows console, or MS-DOS emulators (dosemu & dosbox)
Kempston joystick emulation
Real tape loading through soundblaster
Some screenshots:
Start Screen
Main Menu
Machine Selection
Load from Real Tape
Debug menu