Interactive Colorful Triangle Background with JavaScript and Canvas – Triangles.js
Triangles.js is a standalone JavaScript library which uses canvas 2D API to generate a colorful polygon (triangle, geometric) background with mouse interaction.
JavaScript & CSS background
Responsive Background Image Delivery Using Vanilla JavaScript
bg-responsive.js is a vanilla JavaScript library that allows to intelligently load the appropriate background images based on the screen size you’re viewing on.
Animated Gradient Background with Pure CSS
An animated gradient background using CSS3 box-shadow property and keyframe animations, written in LESS and created by blucube.
Javascript Plugin For Adaptive Image Background Color – Adaptive Backgrounds
Adaptive Backgrounds is a standalone javascript plugin combined with RGBaster.js that allows to extract the dominant color from an image and apply it to the background of its parent element.