HoMM3 HD is a mod (add-on) for the game Heroes of Might and Magic 3.

What else is new besides splitting the stack in half?

Well, there are also some buttons and arrows. Plus, the ability to separate a single unit and transfer it to a neighboring hero. But the most important thing is consistency; I want it to be the same in both Warlords and SoD, as my hands get used to it.