An interesting web service that I conceived and created with a friend. The system tracked orders by users of Amazon.com and alerted them of price changes after purchase. Amazon had a little known policy that said that they would refund the difference if someone bought a product and the price dropped withing 30 days. The users would give us the product, price they paid, and the date they bought it on. If the system spotted a price change within the 30 days, it sent an automated email that prompted them to claim refunds with instructions on the process.
This was the first website of its kind and was profiled in dozens of news outlets including the New York Times, Wall Street Journal, Los Angeles Times and others.
A dozen copycat websites popped up after it and eventually Amazon discontinued the policy.