The division of labour is the sound
Four people playing every note of every chord would be four people in each other's way. What a group agrees on instead — usually without saying anything — is a division: one seat takes the bottom and nothing else, one takes the notes that name the quality, one fills whatever is left, and everybody leaves room for whoever has the melody. Change that division and the same changes sound like a different band.
That is why this site seats four instruments rather than describing an ensemble in the abstract. Each of the four has real reference sections here — every root, every quality, every scale, every key — but the sections are written about the JOB rather than about the instrument, because the instrument itself is taught properly somewhere else.
Two registries, four seats
Three of these seats are strings and one is a keyboard, and in the network's data they come from two entirely different places: a registry of instruments with tunings and string counts, and a registry of keyboards with key ranges and voice budgets. This is the first site in the network to merge the two and draw both, which means the piano here is a full seat with its own diagrams rather than a paragraph about an instrument somebody else covers.
The one honest difference is the section list. A keyboard has no fretboard, so the three fretted seats carry a board explorer and the piano does not — that page is not withheld, it simply would not mean anything. Everything else is identical across all four.
Every seat doors home
None of these four instruments belongs to this site. Guitar Warrior owns the archtop, Bass Warrior owns both basses, Keys Warrior owns the piano, and every single page under every seat carries the link back to its owner at the very same address. That is the arrangement that lets a site about a repertoire serve real reference material without quietly competing with the sites that teach it.