You can get it at
Spaceempires.net in the downloads section of the site. (There is a section dedicated to Adamant as well on this site.)
There is no AI as for now, so you cannot play this mod in singleplayer. Well, you could, but the AI would not do much so.
The premise of Adamant is to choose between three races, Physical ones (such as the ones in SEIV), Organic races (I cannot speak of these) and Magical beings. (Spelljammers!) And then you have quite a few ideas here and there, but I should let Fyron speak of his own mod I guess.
I will have to mention P&N as a very enjoyable mod. (Nomadic races! How to develop an Empire without colonization abilities! And the Pirate clans, although I don't know these much.)