Editors

ed - original editor 

Edits one line at a time.
Modal - edit and control modes. 
Very small memory footprint.
Supports regular expressions.
Highly automatable.
Obsolete for normal editing activities.


nano - user friendly-ish editor. Clone of pico.

Designed primarily for editing email.
Edit area where text is typed in.
Uses cursors to navigate edit area.
Uses [ctrl]key pairs for additional edit features.
Basic help area at bottom of screen with [ctrl]G to view additional help.
Does NOT support regular expressions
Good for editing email, less so for programming.


ex - extended (ed) editor

Many more features.
Usually used via the vi (visual) interface.
Highly automatable - combined with shell scripting to do repetitive edits.


vim,vi - visual editor. vim is the GNU version of vi.

Provides 2 modes, command and edit.
In edit mode, keystrokes become part of the text.
In command mode, keystrokes provide a variety of commands.
[esc] - escape key takes you into command mode.
In command mode, a variety of keys will take back into edit mode.
Very strong support for regular expressions, advanced search, and
  automated editing.
Less friendly than pico but much more powerful.


vimtutor - an interactive tutor.

  Tutor that covers many vi commands.
  Interactive - has user do actual exercises.
  Memory - User can quit and restart at that point.  


Emacs - interactive editor. 

  Almost always text edit mode.
  Uses [ctr]-character and [alt]-character combinations for commands.
  Help has a tutorial.
  User commands coded in LISP which means new actions can be coded by
    users.