(mush) A MUA for Unix and MS-DOS. It has both line-mode and full-screen interfaces as well as a SunView interface.
mush provides a very powerful shell interface with a csh-like scripting language, plenty of environment variables, command-line aliases, filename completion, conditionals, and command piping.
z-mail is a more recent commercial version of mush.
Usenet newsgroup: news:comp.mail.mush.