Writer Grace Spelman collects songs like they're Legos, in a meticulously sorted tackle box. She has over 20 Spotify playlists that trace a specific concept, like False Starts/False Endings, 2000s Dialogue Opening and her magnum opus, Songs for Short Attention Spans, which includes over 200 songs that "totally switch up in the middle". Learn more about her hobby in her video interview with The Outline, above.
Spelman also has plenty of more typical mood playlists, like sleepy music, and songs for feeling over your breakup. She also takes song suggestions over Twitter, so if you know a good horn intro, hit her up.
Metafilter users, impressed by Grace's playlists, thought of some more specific playlists. There's the Truck Driver's Gear Change, a collection of songs with a desperate late-stage key change. There's 4 Chords, a collection of songs using the same super-popular chord progression ripped off of Pachelbel's Canon, as parodied by musical comedy acts Axis of Awesome and Rob Paravonian.
We found a few more around Spotify: Whistling Songs, Songs About Butts, Songs From an Animal's POV, and my favourite, Is This Sufjan Stevens Song Gay Or Just About God. We (I) even have a few of our own, though they're all tiny: Songs about a very specific party, songs that start with a repeated high piano note, and songs with a long-arse spoken-word story. But we could always use more.