[2021] name of the mod that gives you more tiles?

There's one difference between the 25 tiles mods and the 81 tiles mod that is worth noting. The 25 tiles are generated by the game without mods, you just only get to pick 9 of them to use. That means that they are all functional. The outer tiles that 81 tiles unlocks don't exist in the basegame - the mod creates them.

This means that a save using 81 tiles is depending on that mod and if the mod breaks, you might not be able to load your city again. While the 25 tiles mods can be disabled safely and your city will still function.

With both mods the additional tiles become available when you unlock the last milestone.