Working together for free software: Our interview with Protesilaos Stavrou (UPDATED)
My motivations for working on GNU Emacs are practical and ideological.
In terms of practicality, GNU Emacs provides the missing layer of interactivity on top of Unix-y tools. We have a uniform, text-centric interface to the computer, which we can configure and/or extend in a consistent way with the GNU Emacs Lisp programming language. My GNU Emacs setup gives me the best integrated computing environment I have ever had, because I can draw linkages between individual interfaces while reusing code/patterns already established for the rest of GNU Emacs. For instance, a function to indent the selected text in Vim does not automatically become available for text controlled by Tmux. Whereas in GNU Emacs editing and viewing text inside windows are part of a continuum. The consistency of the gestalt form provided by GNU Emacs is not available to the user when they piece together a system out of disparate Unix-y tools.
UPDATE