Just about anything known to mankind.
M-X apropos is a highly useful command in this regard,
you can have emacs search within its commands for keywords.
But in general, emacs can do anything.
Need to work in the Mayan calendar? No problem.
Need to know tides or the phases of the moon? It's there.
Having a bad day? Emacs has a psychoanalyst
mode
.
And if your emacs editor seems to be missing one or
more of these ``highly necessary'' functions, just visit
your favorite tarball/package repository or search engine,
and see if an appropriate package for emacs does not
already exist.