For a manual, it sure as hell doesn't tell me what Maude is.
Fancy seeing this here. I was just writing a paper on formal tools, and made a passing reference to Maude. It's definitely one of the lesser known tools in this area, and confers distinction for an unique approach (rewrite).
There is (certainly there was) a book on same. Indeed, see [1] op's link section 1.6 for that reference.
Now, correct me if am wrong: Maude more than TLA, SPIN, Lean, COQ and the rest of the usual tools has remained far more ensconced entirely in academia. If there's commercial/industrial interest I am all ears.