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

What is HotA?

And seriously, it's an add-on, like WoG.
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The topic is not very relevant (even its latest pages) and will create incorrect impressions. I would say that HotA is an add-on similar to SoD (HotA is contrasted with WoG as a poor collection of various things).
It is better to look here:
Complete description of HotA innovations
HotA 1.2, description and download links