I’m not sure when – or if, or how – Project Zomboid [official site] will ever be finished, as developers The Indie Stone are forever finding new things to add to their open-world zombie survival sandbox. Simulating a world with thousands of characters, players and NPCs, can be a mighty deep rabbit world. DayZ has gotten lost down that hole at times, but Zomboid has at least seemed to be heading towards a finished game.
The next big addition will be a ‘Creative Mode’ which makes creating your own levels far less of a pain in the bum, and will let players do it together online.