I have discovered need of mailing list management capability for a
Sinatra-based site, specifically without licensing restrictions that
would be incompatible with copyfree licenses (e.g. MIT/X11 License, Open
Works License, or Simplified BSD License).  A fair bit of ability to
customize configuration/functionality/whatever in Ruby is desirable.

That means no copyleft, no proprietary, et cetera, and a Ruby API.
Ideally, it would have no dependencies that cannot be gotten via "gem
install foo".  Unfortunately, searching for terms like "mailing list
Ruby", "mailing list Ruby gems", "mailing list Sinatra", or anything
similar tends to lead me to stuff like this mailing list, the Sinatra
mailing list, StackOverflow advice to use Lamson (which has some of the
most malicious licensing I've ever seen, in addition to being Python and
thus unsuitable to my purposes), and so on.

Are there any options out there better than, say, starting near-scratch
with something like TMail that I just haven't found yet?

-- 
Chad Perrin [ original content licensed OWL: http://owl.apotheon.org ]