There are 2 repositories under neo-geo topic.
Simulation only cartridge NeoGeo hardware definition
SNK NeoGeo core for the MiSTer platform
a book on developing for the Neo Geo
Library & toolchain for Neo Geo CD develop. with C language
A Neo Geo Sprite Tile Viewer
FPGA-based PCB to control a YM2610 sound synthesis chip.
A little PCB to buld a SCART cable for console and old computers
fork of the gngeo emulator with a number of bugfixes and modifications
NeoGeo CD intro\demo