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.