Columbia MM (Mail Manager) is an interactive, text-mode mail client for
UNIX, based on the TOPS-20 MM program. It is written in C using the CCMD
(TOPS-20 COMND Jsys in C) package developed at Columbia University.

MM has a lot of  features that appeal to people who deal mainly with
text and who like to keep their hands on the keyboard and work fast. It
is noted for its powerful message selection and management features and
its user-friendly (truly) DEC-20 style command language.