First Rails app built from scratch (ish) with my own solutions for problems encountered along the way. Integrated auto-complete as well as a few other novel features. Learned about asynchronous (not really but visually asynchronous) updates to the DOM, how to use APIs and fleshed out understanding of Rails. However, with the regulatory scrutiny that consumer finance applications face, it's not worth the time to keep working in this direction.
https://github.com/arthurcolle/trophus (private repo)