AMOS is far more capable than it's usually given credit. The problem was it was aimed at beginners so that's what it got. It's not the tool's fault that people typically used it badly!
But "nice" is not a word i would use. Despite my defence of it above, it really is a terrible language. Its main advantage is that it's easy to get started.
I have found the extension source code and an AmigaGuide manual i made for it. Although i just discovered the instructions name-clash with the AMCAF music extension which will cause problems for anyone who has that installed.