Open Source front-end stuff
Built with jQuery and the Twitter Bootstrap CSS framework.
Under the hood, Zotonic uses the CSS framework Bootstrap its templates. It makes building great looking templates a lot easier.
But of course it is optional, you can use your own CSS framework for your own templates without much effort.
For the interaction and Ajaxy stuff we use jQuery. It is an almost industry standard. And one of the few libraries that work reliably on most browsers. You can't disable jQuery. Zotonic will not work without it. Sorry... :-)
And did we mention that you have complete control over your templates?