For a limited time Paradox Interactive is offering Crusader Kings II for free (yours to keep). CK2 is a grand strategy game set in medieval Europe where players use warfare, assassinations, and strategic marriages to attempt to build a dynasty that spans for hundreds of years.
https://www.notebookcheck.net/This-weekend-you-can-get-Crusader-Kings-II-free-to-keep-forever.296482.0.html