Cod is a completion daemon for {bash,fish,zsh}.
It detects usage of --help commands parses their output and generates auto-completions for your shell.

Awesomplete is an ultra lightweight, customizable, simple autocomplete widget with zero dependencies, built with modern standards for modern browsers.

• Awesomplete @ GitHub.

Rich_TextArea is a jQuery plugin replacement for the venerable HTML TEXTAREA that adds arbitrary triggered autocompletes along with the insertion of rich “embedded objects” included images, links, or any other markup.

a fast and fully-featured autocomplete library.

The typeahead.js library consists of 2 components: the suggestion engine, Bloodhound, and the UI view, Typeahead. The suggestion engine is responsible for computing suggestions for a given query. The UI view is responsible for rendering suggestions and handling DOM interactions. Both components can be used separately, but when used together, they can provide a rich typeahead experience.

• typeahead.js @ GitHub.

A jQuery autocomplete plugin for the discerning developer. After spending years struggling with various autocomplete plugins, I became fed up with their bugginess, poor documentation, lack of updates, inflexibility, and antiquated coding patterns. Surely something as fundamental as autocomplete could — really, should — be done better. And now it has. Meet Marco Polo. For the discerning developer.

• Marco Polo @ GitHub.