List of my Gems...

RoR e-commerce 

Validation Issues 

Survey Says 

RoR e-commerce is an ecommerce platform to start a great business with. I've given you a year head start to spin off your own business.

Validation Issues is a great little gem to find out why people are not able to complete your form and hence not convert into paying customers

Survey Says still needs a bit more work but is a great way to score surveys. The Survey can be triggered by other events like "clicking on a product" or "a Purchase" or "an answer to a real survey". Grades can be dynamic so If you find out later that people that do X will probably buy Y you can change the grading scale to the event you are grading. COOL stuff!