You can see a functioning example at: http://louisnk.com/budgeter/
A basic JavaScript / jQuery application to help visualize and plan a monthly budget. It calculates monthly post-tax income based on current (2014) U.S. Federal income tax rates. Adding functionality for other countries is possible with relatively little effort.
Not the most beautiful at this point, but for basic expenses, it works great.
Eventually this may morph into a full-fledged application with database writing capabilities via Node, but that is in the future.
For now, it works for simple budgeting tasks.
The next step is to make all of the fields and blocks dynamic, so that you can choose your own categories and breakdowns, as well as choosing your own colors for each.
This should be completed within a week.