MathLibs was a fun find!
You type in the names of people, objects, and numbers which are used to generate math word problems that cover whole numbers, fractions, decimals, percentages, place value, expanded notation, multiplication, long division, algebraic thinking, geometry, probability and more.
When you get to the site you'll see a welcome message. Select either:
*MathLibs - This is the game generator. Choose grade 3 or 4 and then follow the prompts on the screen to choose a problem "Set." You'll be prompted to type in information to generate word problems.
If you answer incorrectly, you will see the correct answer together with a brief explanation and cartoon animation of how to do the problem.