I started writing a tutorial on fractional reserve banking to help people understand and visualize what it is and how it works.
And, I ended up writing a mini-program to help there, then ended up porting it to the web.
The desktop version (Windows only - .NET 4) is here:
It's very, very simple. The complete source code is available (but keep in mind, it's a tutorial, and not good programming) and free.
And the web edition is here:
Anyways, just a couple stupid little things that you use for a few minutes until you get the idea, then toss away. Hopefully they'll be useful to help some people visualize and understand what fractional reserve banking is.