Its title caught somewhere between the 4X majesty of Endless Space and the interstellar tourism of No Man's Sky, Endless Sky is an open-source, open-world game of exploration, trading, and combat. Inspired by Escape Velocity, it's feature-complete and available to download right now, with free-form rags-to-riches/shuttle-to-battlefleet play fully implemented, and one of three planned stories already in place. As if that weren't enough, there's also an editor and a guide to creating new ships, missions and artwork.
There are Linux, Mac, and Windows builds available right now, and a full manual to help you through your first space quest. I haven't had a chance to try it yet as I'm locked in the rainy city of Satellite Reign, and am planning to visit Fran Bow as soon as I find the exit.
The danger, of course, is that if I were to install Endless Sky I wouldn't resurface for a few weeks. This is like catnip to me. I'd most likely spend all of my time being the interplanetary equivalent of the National Express but this sounds like a dream job:
"The fast, risky road to riches: disabling pirate ships, boarding them, and stealing their cargo and equipment. If you have enough crew members to pilot both ships, you can also try to defeat the enemy ship's crew and capture it. Of course, you can also plunder innocent merchant ships if that's more your style..."
Endless Sky is seeking votes on Steam Greenlight.