I'm like you. I use SourceTree to get a 'visual grasp' on what I find to be the noise of git commands.
However, if you're into command line, you can try fossil: it's got lots going for it.
Your idea of a "user's mental model" might land you into trouble though, because all of us come from different backgrounds (subversion, SSafe, git, HG...) and they all maddeningly redefine terms in different ways (eg branch, forks, commits, checkout).
Your idea of a "user's mental model" might land you into trouble though, because all of us come from different backgrounds (subversion, SSafe, git, HG...) and they all maddeningly redefine terms in different ways (eg branch, forks, commits, checkout).