Since the future of Nvu is Mozilla Composer that will be the basis of
Nvu 2.0, I definitely recommend irc://irc.mozilla.org#composer as the
best spot for discussion on Nvu.

How active is the Composer project?

    Well, it's active ; I spend most of my days on it, a colleague here at Disruptive Innovations is also implementing new features for it, and a few companies have knocked on our door to sponsor it (note to sponsor candidates : please contact us directly, phone is best). A few other people are already working on features or even extensions to Composer. The Mozilla Foundations (Frank Hecker to name him) is actively helping us in our quest for a new name for the project. It is alive and well alive.

What language(s) is Composer implemented in? Is it all C/C++, or is there a higher-level scripting interface also available? I don't suppose there's a Python wrapper?

    It's based on trunk's xulrunner. I think our code additions to the core will represent roughly 20% of the new code, 80% being chrome (xul, js, xbl, css, ...). No, no python wrapper at this time butr that's a neat suggestion.

Is there a home page for the Composer project, separate from SeaMonkey?

    Not yet.

Do I need to check out all of the SeaMonkey source to compile and program Composer, or can it be checked out as a more self-contained project?

    the latter.

What's the best way to start learning the internals? Just check out the source, is there a better way?

    for the time being, yes, the source... I'll document later, I prefer focusing on the code for the time being. Sorry, we're only humans and have limited resources ; in that case, doc is always the part of the project that suffers, unfortunately...