The bundle offers the core rules, the many episodes of The Traveller Adventure, and supplements such as The Spinward Machines.
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We've had a bundle of digital assets from cartographer Alyssa Faden and Frog God on Humble before. The latest deal is twice the size.
Rarely, a physical supplement - Book of Lost Spells - is available, but shipping and associated costs are added later.
Partners in the charity-supporting deal include the talented Alyssa Faden, Tom Cartos, Frog God Games and Cave Geek Art.
$415 worth of downloads is available if you hit that third tier. Frog God and Troll Lord dominate the collection, but titles from Whynot Games, Cave Creek, Pacesetter and Flavor Text can be found.
Frog God Games has an extensive collection of Old School Revival RPGs up at Humble Bundle.
Humble raises money for charities with each deal, and this time the Book Industry Charitable Foundation is getting a slice of the action.
Frog God Games have announced an online games day but warned there will be fewer than 150 tickets available.
The Judges Guild ran a City State of the Invincible Overlord Kickstarter six years ago, and backers are still waiting on their books.