Roon is a software program that does three main things:
Combines your music: It takes all the music you own (on your computer, hard drives, etc.) and all the music you stream (like from Tidal or Qobuz) and puts it all together in one place. You don't have to switch between different apps.
Makes your music experience better: It adds a lot of extra information to your music, like artist biographies, album reviews, and connections between artists. It also displays your music with high quality images. It's like having a super-detailed music encyclopedia.
Plays your music everywhere: It lets you play your music on different speakers and devices around your house, all controlled from one place. It also focuses on making your music sound the best it possibly can.