One of the most interesting things to me about this is the listing of gems/plugins and APIs used for each entry. If it's all in a structured form, it'd be interesting to see a table/list of the most used.
In terms of API, just browsing through, I saw that the Solo winner (http://medpass.es) used a government drug pill identification API I'd never heard of before:
We used Slim for findthin.gs—it's faster, has much better whitespace control, and, imho, better achieves Haml's reduce noise, increase beauty aims. But there's no contest about Sass and CoffeeScript being amazing.