It is a community developed HOMAM3 extension pack, that is being enhanced and has, IMO, many new features while being fully compatible with the game spirit. And they fixed a ton of UI pain points. Coming with a very powerful map editor means that there are community created maps (up to "giant size" -- two steps larger than extra large) that take weeks of challenging play time to conquer.
Pair that with a full HOMAM3 version from "good old games" for about $10 and you will have an unlimited play, no registration, no licensing classic, valid forever. My 2c.