I've always wanted a music player that creates playlists based on your state of mind, but I couldn't find a good one. Musicovery is a site that lets you choose a mood (anywhere from dark to positive and from calm to energetic), a list of genres, a time period, and you get a playlist that can be listened online (in a low bitrate for free).
The songs are visually connected in a graph and when you select a song, the view centers on the current song. This reminds me of MusicPlasma, that shows music artists based on their influence and similarity.
Musicovery doesn't have a huge database, but it's a good option if you miss a dark song from the 90s or you just want to hear a relaxing song.
TNG Edits, "Riker"
53 minutes ago