We've hit sale season pretty hard recently, with various outlets offering interesting ways for us to empty our wallets. Here's another one! Paradox'sis only available until tomorrow, but it's packed with excellent titles.
You can grab (two copies of) War of the Roses: Kingmaker, March of the Eagles, Darkest Hour: A Hearts of Iron Game and Sword of the Stars 2: Enhanced Edition for whatever price you wish to name.
Hit the average price, currently $2.51, and you'll also net yourself Cities in Motion 2 and Warlock: Master of the Arcane. Pay $16 or more and you'll unlock the peerless Crusader Kings 2 and its Russian and Norse Unit DLC. That should keep you going roughly forever.
All of these titles are redeemed through Steam, and only Cities in Motion 2 and Crusader Kings 2 are available for Mac. As usual you can split your money between Humble, developer Paradox and this bundle's chosen charity - charity: water.