Stardock's Sins of a Solar Empire: Rebellion is currently available for free until November 18th from Humble Bundle. All you need to do is subscribe to the Humble Store Newsletter, at which point you can request a Steam key for what is considered one of the better space-based 4X grand strategy titles available. Although the title was originally released in 2012, Stardock has since further polished the game by optimizing the in-game graphics, removing the 2 GB RAM limit, adding larger worlds, better stability and improved mod support in an update back in April of 2017. All these changes made what I would consider a good game better, having played it quite a bit myself. That said if 4X strategy titles interest you give Sins of a Solar Empire: Rebellion a shot, after all, it is free so what do you have to lose?