Humble Bundle's Book Bundle for this month, titled Game Design & Puzzlecraft, includes eBooks and PDFs covering video game, tabletop, and board game design.
Although it seems this particular bundle features mainly tabletop and board game concepts, it may be useful for developers looking to branch out and expand their skill sets through pen-and-paper design.
As standard with how Humble Bundle operates, the Game Design & Puzzlecraft bundle is pay what you want--higher paid tiers include never-before-available new editions of Puzzlecraft, Level Up!: The Guide to Great Video Game Design, A Theory of Fun for Game Design, Women in Tech, and more.
In addition, purchases of every bundle this month go toward supporting Girls Make Games and Girls Who Code, two organizations which focus on developing the skills of young developers through providing workshops and summer programs.
Developers interested in checking out the Game Design & Puzzlecraft bundle can click here.