Macintosh users have several choices of pre-built Emacs. I am aware of the following versions:

* YAMAMOTO Mitsuharu's [Emacs Mac Port](https://github.com/railwaycat/homebrew-emacsmacport)
* David Caldwell's [Emacs for Mac OS X](http://emacsformacosx.com/)
* Vincent Goulet's [Emacs Modified for macOS](https://vigou3.gitlab.io/emacs-modified-macos/)
* David Reitter's [Aquamacs](http://aquamacs.org/)

Some questions I had in mind:

1. Do these versions differ in any signifcant ways?
2. Can one obtain the functionality of the others by simply modifying the initialization file?
3. Do these changes make their way back upstream?

I am aware that Aquamacs is considered "unorthodox" as it has very Mac-like keybindings, but I am also interested in understanding the differences between the non-Aquamacs versions.