mutt next generation (mutt-ng) is a fork of the well-known email client mutt with the goal to both incorporate all the patches that are floating around in the web, and to fix all the other little annoyances of mutt.
mutt-ng contains all the features that can also be found in mutt: we constantly keep the mutt-ng source tree up-to-date with all the changes that happen in the mutt source tree, but also add our own bugfixes and features. A list of features unique to mutt-ng can be found here:
Actually, mutt-ng had many more features that weren't integrated in mutt until the 1.5.7 release, but with this release, the maintainer of mutt quickly decided after months of inactivity to integrate a number of interesting patches, so I will not count those patches to be mutt-ng-specific (anymore).
When migrating from either mutt or an older version of mutt-ng to a newer one, incompatible changes may have been made although we try to avoid that as far as possible. For most users, it's enough to take the old mutt configuration and use it with mutt-ng as both projects still are similar.
As changes are sometimes necessary, they're documented in a document called UPGRADING which is found in the source as well in installed versions of mutt-ng. Please read it carefully upon every update.
Also, you can view it online directly from the project's subversion repository: UPGRADING.
To ease migration in case of variable name changes, the contrib/ directory contains a perl script named update-config.pl which is a dirty hack supposed to update names. If you get warnings or errors reporting that a variable is not known or is scheduled for removal, please use it to update your configuration. It's available online from the subversion repository, too: update-config.pl.
Although there's a complete manual rewrite in progress, there still is an updated "old" manual available:
To provide our users with daily information on what's going on with mutt-ng development, we maintain a weblog with the latest news and other usefull stuff about mutt-ng: mutt-ng.supersized.org
There is no official release yet, but you can download daily snapshots from the snapshots directory or check out the latest source from the SVN repository (Subversion required).
Christian Schneider had been so kind to build a wiki page for mutt-ng. You will find it here: http://www.strcat.de/muttng.
To give feedback about mutt-ng, there's a number of possibilities: