Free on Steam: https://store.steampowered.com/app/236870/HITMAN/
Also free on PS4: https://store.playstation.com/en-gb/product/EP0082-CUSA02369_00-00000OCTOBERPACK
And Xbox One: https://www.microsoft.com/en-gb/p/hitman-halloween-pack/c0p287tqfzmr#activetab=pivot:overviewtab