A simple ZX Spectrum 48K Libretro core based on the chips toolbox. The core can only open Z80 files, and doesn't support save states.
A very simple Makefile is provided, type make to create the core. If that doesn't work please submit a PR, the only file that has to be compiled and linked is src/main.c.
src/main.c is MIT, the other files in src/ are licensed under the Zlib license.