Those who purchased To the Moon direct from Freebird Games' website can snag the Steam version for free by sending an email with your order ID to steam [at] freebirdgames [dot] com. Developer Kan Gao is manually sending out Steam keys once he gets them and he asks for patience in this process.
Freebird is working on the second episode of To the Moon and a "short game set in the same universe before that," Gao says. He offers a preview of a song from one of these games right here.
To the Moon comes highly recommended from some of the people you trust most in the world.