Based on the concept of physical manipulatives such as blocks and Cuisenaire rods , manipulatives are physical objects which embody abstract mathematical concepts. Virtual ones are virtual representations of physical objects which embody abstract concepts


http://mathworld.wolfram.com/topics/AnimatedGIFs.html Brilliant! Animated GIF's illustrate a large number of mathematics concepts.
http://nlvm.usu.edu/en/nav/vlibrary.html National Library of Virtual Manipulatives
http://www.fi.uu.nl/wisweb/en/welcome.html WisWeb is the website of the Freudenthal Institute for secondary education (students of 12 to 18 years old). The main focus of the site are applets; small computer programs that run over the internet
http://www.shodor.org/interactivate/activities/index.html These activities are designed for either group or individual exploration into concepts from middle school mathematics. The activities are Java applets and as such require a java-capable browser.
http://www.levitated.net Levitated.net contains visual poetry and science fun narrated in an object oriented graphic environment, open source Flash modules