I made this as a gag application one lazy afternoon this past summer.
What it does
The application actively listens to what you say, transcribes it into text, and searches that text for one of any predefined curse words, and plays a loud tone when it hears one.
What did I learn
I learned how to use and interact with Swift's SFSpeechRecognizer and AVAudio player, which I plan to use in future more complex applications.