If you're part of the maker community, you know Make:. Though Make: magazine is off the shelves as of this year, the eBooks and resources put out by Maker Media are still a fantastic resource for the new generation of tinkerers, hackers, and robotics geeks.
If you're in that tribe, listen up: they've released a bundle of eBooks on open-source electronics, and the entire 15-volume package is on sale on a "pay what you want" basis.
There's a wide range of knowledge here, and a lot of covers the possibilities of the Arduino platform. You'll get everything from ground-level Arduino 101 primers to in-depth blueprints for atmospheric monitoring devices. You'll also get books that dive into Arduino-compatible gadgets like Adafruit's Trinket board, while overviews teach you how to tie all this tech together to make your own inroads into robotics, home automation and the Internet of Things.
There are 15 books in all with a total value of $277.85, and you can pick them up for potential pennies. Just name your price – any amount will take home something, and you can get the entire package by beating the average price.