It’s really spelled 真Gnus. Ma Gnus was the code name for the development version of Gnus started in 2012. These days, Gnus is only released together with Emacs.
New features in Ma Gnus:
gnus-gcc-pre-body-encode-hook
and
gnus-gcc-post-body-encode-hook
are run before/after encoding
the message body of the Gcc copy of a sent message.
See Archived Messages.
For more recent changes, see the Emacs NEWS files.