Race the Sun includes the Simplex World Creator for making your own custom worlds, and we are in the process of adding Steam Workshop support. With Workshop you will be able to rate and play other player-created worlds, as well as share your own. We will also be tying the in-game world portals (the big green ones) to the best user-created worlds! When this is all set up, flying into a portal could take you anywhere!
Soon we will be opening up a beta version with Workshop support, so be on the lookout for that announcement.
We are also finishing up the Linux version of Race the Sun for Steam - just a few bugs to work out and it will be ready.
Thank you all for your thoughts and feedback as we update, fix and improve Race the Sun!
- The Flippfly Team