Starsector. Been described as "Mount & Blade in space", which I think is still pretty apt. Made mostly by one guy, been in development for years. Still getting regular, substantive updates, has an awesome modding community with full developer support that adds tons of great content to the base game. Can't recommend it enough.
Yesterday I sat outside in the yard with my dog and read a book for like six hours. One of many reasons I'm not going back to reddit.