I made software using JavaScript that has about 300 songs and the software mixes the tempo matched instrumentals in key, each refresh creates a new endless mix and its powered by the super accurate Web Audio API hardware clock, even works on iOS.
The dopest part is that it is super flawless accurate as far as key matching and tempo matching goes and its all written in vanilla JavaScript. It even does some things DJs cant currently do, like considering the accurate tempo/pitch shifted key (like when a DJ speeds up a song) instead of the one the song is recorded at. As much fun as DJing has been to me for over 20 years, this is even more fun because it comes up with combinations I love and have never used before but they sound great together.