Our game, "1Minute" has several (ironically) only one elements, with better or worse execution.
The original premise for our project was to use one button and make a rhythm game with it. In the end after brainstorming we ended up making a game where you type using a telegraph.
The character is alone on his room. He has one arm. He has a telegraph and a morse code manual, but can only use one at a time. The color palette is centered around one tone. The music you hear while playing is designed around one note and uses only C for the melody. The premise is kinda based on WW1, but we opted for using an aseptic war, with ni real bands or anything.
Ah, also, you have to send one message and have one minute to do it. If you do so, you stop a chemical bomb from being dropped on your country.