Humble Bundle have announced that throughout this week, they will be sticking up older popular bundles for a very limited time and limited amount of purchases so keep an eye for some fun hits to stock up on.
The first is the 2K Megahits collection that contains XCOM Ultimate Edition (XCOM + XCOM 2 + Chimera Squad), X-COM Complete Pack (the classics), Borderlands 3, Civilization VI, BioShock: The Collection, Mafia: Definitive Edition, Railroad Tycoon 2 Platinum, Railroad Tycoon 3, WWE 2K Battlegrounds, CivCity: Rome, Hidden & Dangerous, Hidden and Dangerous 2, Army Men RTS and Duke Nukem Forever Collection. For this bundle they do note that some keys aren't yet available but will be restocked sometime soon.
So it's a little like Fanatical's Bundle Fest that they do each year. Seems like a nice easy way to build up your game collection this week ready for the holiday season.
Keep an eye on their Bundles Page each day for something different.