Songs in the Key of Z, Vol. 1 [2000]: a compilation of ‘outsider music’

I.e. music by people not too concerned with usual formal requirements for music.

Also:

‘Songs in the Key of Z, Vol. 2’ (2002) — both of the first two volumes served as companion records for the book by Irwin Chusid.

Vol. 3 and Vol. 4 — compiled separately and released in 2013.