Aside from the obvious minecraft... Arguably I'd say Factorio. They have a robust, feature-rich modding API built into the game that allows for relatively easy, wide ranging game play mods to be made very stable, and the number of mods has exploded as a result. The base game is amazing, but mods exist that quite literally triple the amount of game play and in some cases completely overhaul it into a totally new game. The support is amazing, and I wish more game companies could operate as efficiently as Wube does.