RequireJS
A file and module loader for JavaScript
Head js
The only script in your HEAD. Head JS loads JavaScript files in parallel like images without blocking the page. Your page will be faster. Even with a single combined file.
Layzr.js
A small, fast, modern, and dependency-free library for lazy loading.
LABjs
Loading And Blocking JavaScript: On-demand parallel loader for JavaScript with execution order dependencies
Script.js
Asyncronous JavaScript loader and dependency manager
Webpack
Packs CommonJs/AMD modules for the browser. Allows to split your codebase into multiple bundles, which can be loaded on demand. Support loaders to preprocess files, i.e. json, jade, coffee, css, less, ... and your custom stuff.