2. Yahoo! UI Library – This is different from the Google Web Toolkit in that it isn’t meant for a specific server-side environment. The Yahoo! UI Library gives developers tools to quickly create cross-browser user interface components. It has some nice widgets for drop down menus, drag and drop, and animation. The UI Library also features some nice css layout managers as well as css normalizing files. You can pick and choose which parts you want to use in your application. If you want some quick, standard 2 column layout templates, the UI Libraries are great. The Connection Manager also provides some nice libraries for performing asynchronous calls to your back-end server.