JSXGraph is easy to embed and has a small footprint: only about 80 KB if embedded in a web page. No plug-ins are required!
JSXGraph is developed at the Lehrstuhl für Mathematik und ihre Didaktik, University of Bayreuth, Germany.
You do find a big compilation of showcases and examples at the JSXGraph Examples-Section.
You find questions and answers in the related Google group:
JSXGraph Google Group