What is a project you could build over a weekend?

This weekend @iamgdsa and myself decided to do a hackathon to see what we can build in 48 hours. As we recently moved to Portugal, we wanted to learn Portuguese and built a beautiful Language Flashcard app in 19 languages with audio for each word in that respective lanaguage. Mindblown how something like this would have taken 2 weeks of data gathering, now just takes a day.