And by “a limited time,” they mean just under two days as of this post. Here’s their store page for Wasteland 2, and I give it a recommend if you like party-based computer role-playing games. It’s got more polished in-game animation than the original Fallout games, but the “cutscenes” are a little slide-showy. It’s got some decisions for you to make, plot twists involving various party members, and a showdown at the end that can be made easier or more difficult depending on the actions you took getting there.
It’s worth playing, especially for free. I’m guessing it’s to generate buzz for the upcoming Wasteland 3, whose release date is “early 2020”:
I think the in-game lore is just that at some point, a military facility (pre- or post-war) decided that robotic arachnids was the key to ruling the battlefield and put them into mass production (even spilling over into Fallout New Vegas’ DLC, Old World Blues).
I may also have to add that trailer’s version of “Land of Confusion” to my playlist. If you want to hear it without all the explosions and narration, here it is.