simplebox.js is a lightweight lightbox plugin (936 bytes) that is easy to modify or extend to fit your needs. This plugin is intended to be a quick, responsive, efficient. Here's a a quick demo showcasing simplebox.
Give it a go
The idea behind this plugin was to make setting up lightbox painless. My experience with finding and setting up lightbox plugins has been pretty bad. The plugins I've come across almost always have too many features. simplebox.js is designed to have just one feature: lightboxing. It's responsive out of the box and allows only a few crucial settings. Think of the minimalism as feature and not a drawback!
Check out the documentation for simplebox.js on GitHub.