I have been working on developing some interactive tools for demonstrating statistical principles. The advent of the shiny framework for R from the RStudio team has made this very easy to do. These demos are still in the development stage, but they are designed to help refresh statistical knowledge for applied folks now working more and more with data in their jobs.
A link to each demo online, where you can use it, and a link to the code so you can run it on your local machine or clone it and modify it on your own is below. There is also the R code to run the demo locally on your machine.
Moments of Distributions