Published by National Council of Teachers of Mathematics (US) and the MarcoPolo Education Foundation
This site has enormous variety of quality online materials and links for teaching and professional development. It will take some time to really explore the extent of what is available here, but its well worth the effort – and made easier by the capacity to browse by approximate grade level or type of resource.
Activities include Java applets, online interactive multimedia mathematics investigations, links to Internet resources on other sites (reviewed by an editorial panel), and professional development materials. Suitable for early childhood to senior secondary.
Published by Utah State University (US) with support from the National Science Foundation
This site has a wonderful collection of interactive, web-based tools and tutorials, mostly in the form of Java applets for student use. Activities include an extensive collection of games and activities involving the manipulation of virtual objects, many of which are derived from classroom counterparts such as pattern blocks, geoboards and tangrams. It also has a large number of attractive and engaging activities that allow teachers to readily identify appropriate materials. The activities are sorted by both mathematical content and by approximate grade level, and many are ideal for encouraging open-ended student exploration. Suitable for early childhood to senior secondary.
Published by The Shodor Education Foundation, Inc. (US)
The goals of the Interactivate site are “the creation, collection, evaluation and dissemination of interactive java-based courseware for exploration in science and mathematics.” This site contains more than 100 interactive tools and activities, together with background and support materials (including a dictionary of terms) and suggestions for lesson plans. Many of the “tools” are general purpose applets with multiple uses (including such things as random number generators, a stopwatch, game spinners etc).
Presentation of the activities is in a format which is uncluttered but provides ready access to instructions and supporting materials. Suitable for middle primary through to secondary.
Published by Drexel University (US)
Ask Dr Math is an e-mail ask-an-expert service for questions about mathematics (with the best questions and answers also organised into a searchable archive).