Base 5 Blocks
Here you can represent numbers in base 5 using "blocks". Each "unit" is 1, a "long" is 5, and a "flat" is 25. You can change the numbers, put and take apart the different blocks, and use this to see how to count, add, and subtract in different operations.
Note: This app was adjusted from John Golden's app: Base 10 Blocks at www.geogebra.org/m/RhjKaUgB. Thank you!