jQuery Tools library is not a framework with a steep learning curve, lots of preliminary work and strict coding rules. You are not tied to any predefined HTML or CSS structures. You can include the library on your pages and start using it immediately. If you want modify default behavior of any component, it offers comprehensive API for easy customization.
This library is open source and dual licensed under MIT and GPL 2+ licenses. You can find further information, demos, API documentation & download on jQuery Tools’ Website.