alt Hacker NewsVideo games in general have lots of people working on their games for decades too. UnReal World is from early 90s, was released on Steam in 2016, and AFAIK still gets updates. Nethack is even older (late 80s?) and also still get updates, I guess there might be bunch of MUD with single creators who still churn out updates too. Dwarf Fortress is quite old too for still gaining in popularity.
Oh video games in general can have crazy development times, whether it's through an open beta/development process or a closed one. Dwarf Fortress is a good one for sure, as is Star Citizen. Also Duke Nukem Forever, and Beyond Good & Evil 2 (the latter has somehow passed the former's record for longest recognised game development time at 20 years compared to 14).
Super Mario Bros X is arguably getting up there too, started in 2009 by Terraria developer Redigit, and now in development by a new group as of 2026.
And while a Doom fan needs to check this, I remember the mod Mordeth started before Duke Nukem Forever was announced, and the later episodes ain't done as of 2026.