An online visualization tool for sorting algorithms.
Ahh, sorting... The most over-studied concept in the undergraduate computer science curriculum. Then, why is this solved problem so important? First, it is a good introduction to algorithm analysis and problem-solving. Secondly, the variety of sorting strategies is HUGE. There are algorithms useful for each type of situation. Some are more efficient memory-wise, while others are more efficient based on their runtime.
Thus, the purpose of this tool: to help students (and curious learners) visualize how these algorithms work.
Happy Sorting!