Polypad.

Number Frames help students structure numbers to five, ten, twenty, and one hundred. Students use the frames to count, represent, compare, and compute with numbers in a particular range. The frames help students see quantities as equal groups of other quantities and in relation to benchmark quantities. This helps primary students move away from one-by-one counting toward more efficient ways of counting and computing. As students advance, custom frames can be constructed to help visualize factors, products, fractional parts and more.

With this tool, students can place different weights on a balance to compare numbers.

Mathigon offers interactive mathematic courses that cover the primary and secondary math program. The website also contains online activities and games to practice math concepts. Finally, the Polypad is a tool to create different mathematic representations to help visualise math concepts. [Source : Mathigon website]