This is an online version of the old card game Concentration. You play by turning over cards, one at a time, and looking to match the symbols on the other side. When you match cards, the background color changes and they stay turned over. Otherwise, both cards turn face down and you can choose again.
The game ends when you find all of the matching pairs.
At the moment, I am the only person allowed to contribute to this project, as it is an assignment for earning a Front-End Nanodegree from Udacity. But feel free to request changes or improvements through the issues interface.