Adventure Expansion is an add-on that focuses on expanding upon the exploration, player vs environment, adventure side of the game by adding new materials, structures with unique loot, creatively crafted mobs and bosses and much more.
Release 1.0 is the real deal, shifting over to new designs and much more quality in mind.
This is also the last update Adventure Expansion will get. (A small chance that this may turn into "for a long time", don't count on it).