Probably one of the best spaceship building sandbox games around, Avorion has just grown tremendously with the Into The Rift DLC out now.
In this hardcore add-on you'll explore the mysterious and dangerous Rift dimension. Thanks to new technology, it is now possible to send smaller amounts of mass (i.e. a few ships) into the Rifts. Scientists are now intensively researching these Rifts - and they need your help. Travel into the Rifts and uncover their secrets. Face their dangers, complete research expeditions, and earn powerful new rewards. This arrives along with a big version 2.2 patch for all players.
- Discover a new dimension unlike anything you've seen before in the galaxy.
- Prepare your ship accordingly to master the dangerous new environments and uncover the secrets surrounding the origins of the Rifts.
- Complete Rift Expeditions for the Rift Research Center, and receive new, powerful hybrid subsystems in return - or simply keep everything you find in the Rifts.
- Remember, the deeper you venture into the Rifts, the more lucrative and dangerous they become.
- New story campaign.
- New captain classes.
- + Loads more
I'm surprised this one doesn't have a lot more players. With a Very Positive rating on Steam, along with gameplay that offers a good mixture of spaceship building and exploration, there's a lot to enjoy with it. It regularly sees around 2,000 players online at the same time each day and you can play it alone or with others. Native Linux support too and it works really nicely.