Aquamacs is an Aqua-native build of the powerful Emacs text editor. By "Aqua-native," we mean more than just the fact that this version of Emacs runs as a standard OS X application.  Aquamacs features extensive customization that enables it to conform better with Apple's standard Human Interface Guidelines (HIG) than standard versions of the editor do.

Why use Aquamacs?

Why use Aquamacs instead of the a stock Carbon or X11 Emacs on the Mac? Here are some features that Aquamacs has to offer:

• Fonts just work, right from the menu: The Mac-standard font (Lucida Grande) is the default for editing text, and the mono-spaced Monaco is used to other modes. These fonts are nicely rendered with antialiasing. Aquamacs offers a range of proportional and mono-spaced fonts to choose from.
• Emacs has a standard Mac menu with entries where you would expect them, and recently used files are available from the File menu.
• Aquamacs Emacs opens a normal OS X window for each file that is opened - Emacs experts call the windows frames. Finally, Emacs makes use of the capabilities of windows on modern graphical user interfaces.
• You can switch between the windows (frames) with the "Buffers"  menu.
• Clipboard operations interoperate with other Mac apps. In the  Aquamacs version of Emacs, if you mark a chunk of text, it will NOT be automatically copied into the clipboard. Just like in any Mac  program, you can copy with the Apple-C command, and then replace  another region by selecting it and hitting Apple-V (Paste).
• You can define fonts and colors as defaults for a given editing mode. That means that you can have customized designs for different types of files you're editing. For example, you can easily distinguish LaTeX files on the screen by htheir beige background color.
• A number of little extensions specific to the Mac are supported - they're small details that make your life easier. For example, there is a "Show (file) in Finder" function. Aquamacs Emacs is available from the Finder context menus, and when you double-click a file written in Emacs, it'll open in Emacs (thanks to Creator meta-information in files).
• Emacs remains extensible, so you can use special syntax coloring setups or enjoy embedded CVS support, a HTML markup menu and the like.
• Aquamacs offers a dedicated manual plus the good old Emacs manual directly via Apple Help environment - you can search it quickly with Spotlight and read the documentation comfortably.