The NeoGeo hardware as it is known is an upgrade of Alpha Denshi's Alpha68k design from 1986. Simply put, it seems that Alpha Denshi (ADK) were the hardware guys, while SNK took care of the games (and money for a while).
The main upgrades were:
- Increased horizontal resolution (256 to 320 pixels)
- Sprite shrink capability
- Better soundchip (YM2203 or YM2413 to YM2610
- Faster CPU clock (8MHz to 12MHz)
- Board size reduction by using custom chips
The Alpha68k mainly used off-the-shelf logic chips which reveals lots of the NeoGeo's GPU design. The only custom chips used were an early version of PRO-CT0 and SNK-CLK, which provided video timing signals. The graphics data formats used on both systems are exactly the same.
South-Korean company Andamiro produced the gambling-oriented Midas 2D system around 1999, which uses the same video logic as the NeoGeo but with a higher color resolution. See MAME's midas.cpp.
It is unknown if the design was sold or if it was "inspired from".