Did you make it through all of Creative Scala? Great job! Your path to Scala knowledge is only getting started.
Here are some ideas of other things you can build to expand on what you just learned:
Use Doodle to build a hangman style game (hint: you can play by accepting user input)
Create a Markov Chain Generator
Grab source material from Twitter, Wikipedia, Project Gutenberg
Parse a Twitter stream to find interesting trends in the data
Build a Slack bot