A single-page app made in Elm with a Go backend that scrapped estantevirtual.com.br in real-time for search results of multiple different search terms and aggregated the results per book store, so when you want to buy many books you can find the stores that have the biggest part of what you want and buy everything together, paying less for the delivery fee.
It had a very weird unicode issue I never managed to solve, something with the encoding estantevirtual.com.br used.
I also planned to build the entire checkout flow directly in this UI, but then decided it wasn't worth it. The search flow only was already good enough.