- - jQuery is the most popular Web-based alternative to Prototype JS.
- - jQuery is the most popular Open Source & free alternative to Prototype JS.
- - DHTMLX is the most popular commercial alternative to Prototype JS.
- - YUI is the most popular Windows, Mac & Linux alternative to Prototype JS.
Per website: "IMPORTANT: The YUI library is no longer actively maintained."See http://yuilibrary.com/