RetroAchievements
This community is unofficial. Let me know if a developer of RetroAchievements wishes to have a Lemmy community.
RetroAchievements is a service that adds achievements to old games! From Gameboy to PlayStation 2 to the TurboGrafx-CD, regular and challenge achievement sets are available across myriad games and game hacks.
The achievement system is baked into specific emulators, and requires nothing more than the proper ROM or ISO and your user credentials to start earning.
I'm really interested in the Professor Oak Challenge subsets for the Pokemon games, but my favourite set I've seen was Kingdom Hearts: Chain of Memories [GBA], since it gives each boss a really good challenge achievement. Things like limiting the attacks you can do, types of attacks you can do, if you can move. It's really interesting (and difficult!)