During set-up, you place 5-7 colony tiles in play from the eleven included in the expansion. On a turn, in addition to any of the other actions, you can spend 17 M€ to build on a colony and take its particular bonus, with only three players being able to do so, or you can spend 9 M€ (or three energy or titanium) to move your trade fleet to a colony tile and take the trade income posted there, with each owner of a colony on that tile receiving a colony bonus.
The expansion also includes 49 project cards to be shuffled with those in the base game.
• In March 2018, designer Tom Lehmann gave a talk at the 2018 Game Developers Conference on how to design a strategic card game, using Race for the Galaxy for reference. During that hour-long talk, he threw out a couple of references to New Frontiers, which at least in the images shown during that talk is subtitled "The Race for the Galaxy Board Game".
Now Lehmann has dropped an introductory teaser for New Frontiers on BGG, along with a picture showing prototype worlds, developments, and empire mat, along with production quality goods and colonists. An excerpt of the game description in that thread:
In New Frontiers, players build galactic empires by selecting, in turn, an action that everyone may do, with only the selecting player gaining that action's bonus.
One group of 8 developments are always in play, giving the game its core structure. For your first game, the other developments have "preset" sides. In later games, which of the other 8 two-sided "small" developments and 8 two-sided "large" 9-cost developments will be in play is randomly determined during setup for that game. This provides variety from game to game, while allowing players to make strategic plans based on the developments in play at the start of each specific game.