This virtual manipulative uses plus-minus chips to demonstrate adding positive and negative values.
http://nlvm.usu.edu/en/nav/frames_asid_162_g_3_t_1.html?open=instruction...

The goal of this puzzle is to put three numbers inside of each circle so that they add up to 99.
http://nlvm.usu.edu/en/nav/frames_asid_269_g_3_t_1.html?open=instruction...

The goal of this puzzle is to put three decimal numbers inside of each circle so that they add up to 3.
http://nlvm.usu.edu/en/nav/frames_asid_187_g_3_t_1.html?open=instruction...

The goal of this puzzle is to put three numbers inside of each circle so that they add up to 0.
http://nlvm.usu.edu/en/nav/frames_asid_122_g_3_t_1.html?open=instruction...

A snazzy virtual geoboard. You can teach just about any topic with a geoboard. If you don't have a class set of the real thing, get one!
http://nlvm.usu.edu/en/nav/frames_asid_125_g_1_t_4.html?open=activities&...

With this virtual manipulative you can create objects with pattern block pieces and explore Translations ("Slides") as transformations of the plane.
http://nlvm.usu.edu/en/nav/frames_asid_167_g_1_t_3.html?open=activities&...

With this virtual manipulative you can create objects with pattern block pieces and explore Rotations ("Turns") as transformations of the plane.
http://nlvm.usu.edu/en/nav/frames_asid_207_g_1_t_3.html?open=activities&...

With this virtual manipulative you can create objects with pattern block pieces and explore Reflections as transformations of the plane.
http://nlvm.usu.edu/en/nav/frames_asid_206_g_1_t_3.html?open=activities&...

Choose some shapes and try to tesselate the plane with them.
http://nlvm.usu.edu/en/nav/frames_asid_163_g_1_t_3.html?open=activities&...

Tangrams are a versatile manipulative. They can be used to build understanding of geometry, fractions, area and other topics. This is a Java implementation of tangrams.
http://nlvm.usu.edu/en/nav/frames_asid_268_g_1_t_3.html?open=activities&...