This is the most powerful editor ever to exist . Most of the people use GNU Emacs. It is build on lisp, the artificial intelligence programming language. It has been favorite of many hardcore Linux users amd programmers. Emacs at first was made by Richard M Stallman and was the first program of GNU. It has fought the great wars with vi called editor's wars ( its a tech term).
But it must be noted that emacs is not for beginner and many developer also don't bother with using it. It has both command line and gui mode. A fork of it exists called Xemacs.

It can be used as an IDE also.
emacs filename

Ctrl+x quit

Ctrl+s save

It has many advanced features like buffer manipulations which will take too long a time to write and I also don't know all.

man emacs for more info.