Lemma is an exploration game; you explore and piece together the story, and of course you do a lot of parkour. You play as Joan Emerson, a physics grad student whose colleague Mark hits a breakthrough and disappears into the mysterious world of Lemma.
Planets³ an Open-world Voxel Sandbox Game that you should check out and back on Kickstarter
Pathea Games the developer of Planet Explorers have released a new alpha build of Planet Explorers. You can try the demo of the game with 2-3 hour gameplay for free on Mac, Windows and Linux.