What does abandonware mean?
Technically, abandonware games are games not supported anymore from their developers. If the original developer company is no more and if the game is so old that no one cares for it anymore, it becomes "abandoned".
Usually, no one bothers about abandoned games but the retro gaming community, that's why it's so easy to find online games developed for now defuct platforms like Commodore 64, MS DOS, Sega Genesis, Windows 3.1, Spectrum, Amstrad CPC, etc.
There were so many different home computers and consoles in the 80s and the 90s that abandonware became a niche phenomenon.
If you're into abandonware for DOS and Windows, take a look at Abandonware DOS, my other project.