Design your very own QR codes with QR Designer. This is a web application for creating customized QR codes, there is no dependency of an external service, all the customizations and generations are done on the client thus it even works when you're offline.
A bookmarklet that generates a heatmap on the HackerNews frontpage so users can see what are the hot topics. Heatmap calculations are based on points or comments count. I created it in order to inspire users to make cool stuff with heatmap.js and they did :)