A guy named Richard Stallman started preaching the gospel in the early '80s, though he called it free software. Linus Torvalds started work on Linux, the enormously successful open source operating system, in 1991, and today, it drives our daily lives—literally. The Android operating system that runs so many Google phones is based on Linux. When you open a phone app like Twitter or Facebook and pull down all those tweets and status updates, you're tapping into massive computer data centers filled with hundreds of Linux machines. Linux is the foundation of the Internet.

And yet 2015 was the year open source software gained new significance, thanks to Apple and Google and Elon Musk. Now more than ever, even the most powerful tech companies and entrepreneurs are freely sharing the code underlying their latest technologies. They recognize this will accelerate not only the progress of technology as a whole, but their own progress as well. It's altruism with self-interest. And it's how the tech world now works.