The FastLED library is a popular library for easily and efficiently controlling a wide variety of pixel-addressable RGB LED chipsets, like the WS2812, APA102, and others. Use this tag for questions specifically about FastLED usage and development.
FastLED is a library for easily and efficiently controlling a wide variety of RGB, pixel-addressable LED chipsets, like the ones sold by AdaFruit under the brand names Neopixel and DotStar. These chips let you send an RGB color to a chip which contains red, blue, and green LEDs and they maintain that color. Popular LED chips include the WS2812b and family, the APA102c, and a bunch of related chips. Typically you control them by hooking them up to an Arduino or similar controller, programmed in C++, and send strings of bits through an output pin to the chips to specify the colors you want.
FastLED makes it easy to define an array of RGB colors, update it, and send it to your LEDs quickly.
In addition to writing to the LEDs, this library also includes a number of functions for high-performing 8-bit math for manipulating your RGB values, as well as low level classes for abstracting out access to pins and SPI hardware, while still keeping things as fast as possible. Tested with Arduino up to 1.6.5 from arduino.cc.
Advantages of FastLED:
Quick start for new developers - hook up your LEDs and go, no need to think about specifics of the led chipsets being used
Zero pain switching LED chipsets - you get some new LEDs that the library supports, just change the definition of LEDs you're using, et. voila! Your code is running with the new LEDs.
High performance - with features like zero cost global brightness scaling, high performance 8-bit math for RGB manipulation, and some of the fastest bit-bang'd SPI support around, FastLED wants to keep as many CPU cycles available for your LED patterns as possible.