A few years ago I had the opportunity to work on the NSF-funded "Dynamic Number" project led by Daniel Scher. Our objective was to bring the interactivity and fun of dynamic geometry to the realm of numbers and pre--algebra, and we produced about 70 activities, many of which can be very helpful in developing students' number sense, both by providing memorable dynamic visualization of numbers and operations, and by giving students the power to change the numbers and manipulate the operations.
Each activity has a link to teacher notes, a student worksheet (if appropriate), and a Sketchpad document. Though the activities were originally developed for The Geometer's Sketchpad, Daniel has already moved more than 40 of the activities to Web Sketchpad, making them freely available even if you don't have Sketchpad itself. The list of converted activities is here: www.sineofthetimes.org/...
(One of our best examples is Bunny Times, with a progression of levels in which a bunny, and at higher levels a team of bunnies, learn to multiply by eating all the carrots in a field. It's designed to encourage students to develop multiplication strategies that include skip-counting and flexibly composing and decomposing numbers.)
*Taken from https://my.nctm.org/home