Here’s a nice discovery from deep in the web. Singer/songwriter John Martyn, OBE used many altered tunings over his 20-plus album discography and the late guitarist’s website outlines many of them. Aside from common scordatura such as Drop D and DADGAD, you’ll find examples like the title track from Solid Air, tuned CGEbFBbD—half C minor, half Bb. Dig in and take a look at them all.

Right here.