A plugin for Spotify that enable you to label music with emotions and sentiments of how you perceive them. While doing so, it gets to learn what you love/hate, what makes you relax/productive, etc Qualify your music with emotions. What excites, what makes you calm down?
The Emoqual app uses this information to make you progress faster in any training program through the power of music. The training program pushes you forward but adapts both the music and program on the fly based on your specific situation and heartbeat. This can be used for all kinds of sports, but athletics, running and cycling seem the most obvious to me.