Aquamacs 2.5 – Emacs editor with aqua GUI. (Free)

Aquamacs is the Emacs editor that Mac users love. Aquamacs lets you write text from LaTeX manuscripts to to-do lists, from C to Cobol, Java, Python, Shell-script, Lisp, everything! Aquamacs looks and behaves like other Mac programs – even though it’s still the powerful GNU Emacs with all the extensibility that millions have come to appreciate.

Emacs is a text editor of legendary power and configurability, but it also has an enormously complex interface. Aquamacs tames the Emacs tiger: you get Apple shortcuts (in addition to the Emacs ones), nice fonts, one file per window (if wanted), international input methods, Apple Help manuals and more. Aquamacs comes with a range of modes for various markup and programming languages: HTML, C/C++, Java, Python, Perl, AppleScript, Tcl, XML, R (S)… These modes have extra functions for the languages, including excellent syntax highlighting. You can even use Aquamacs to read news and e-mail, just like any Emacs.

Version 2.5:

Aquamacs is now signed and will now execute with the default GateKeeper settings in OS X 10.8.
Full-screen now supports the standard OS X 10.7 “Lion” full-screen mode: The frame takes up the full (main) display and uses its own screen. Users may switch between screens as usual (mouse swipe or C-left/right, for instance). The old-style fullscreen mode is still available, however. To maximize a frame on the current space, allowing other frames on this space, type C-u A-S-Return, or prepend any of the commands that enter fullscreen mode with C-u.
Retina displays are now supported (high-resolution artwork is included in most cases). LaTeX Preview mode (AUCTeX) has been modified to show high-resolution previews. (Technical note: other packages can be updated by providing TIFFs with multiple resolutions, or by generating high-DPI images, setting their DPI meta information correctly, and setting the new ‘ns-true-dpi-images-filename-string’ variable while loading images.)
S-tab no longer mapped to C-y (ASCII 25, end of medium). Now properly handled as backtab.
Aquamacs now provides experimental session persistency: you can load and save sessions. Use the new Load Session, Save Session As menu entries in the File menu to use these new functions. Note: Unlike the formerly available functions from the ‘desktop’ package, all frames, windows, tabs, buffers and some customizations are saved. Buffers not linked to a file, such as those showing processes, will not be restored, and frames may not end up on the same space at this time. Aquamacs now includes an adapted version of the revive.el package by Hirose Yuuji. We recommend that you do not load a different version of this package yourself.
Colors are now displayed in the “color space” that is set by the user for the specific display. A slight change in color shades may be noticed.
Text search (isearch) now works better when using one of the Emulate-Mac-Keyboard-Modes.
Frames are now reliably moved inside the current display again when entering the minibuffer (and at other times).
Switching applications while Aquamacs is in full-screen mode no longer creates unwanted empty frames.
ESS upgraded to 13.05. (Previous version was 5.13 – no joke. The ESS version numbering changed.) See here for changes: http://ess.r-project.org/Manual/ess.html#New-features
AUCTeX upgraded to 11.87. (Previous version was 11.86.) See here for changes: http://www.gnu.org/software/auctex/manual/auctex/Changes.html
Python-mode upgraded to 6.0.8. (Previous version was 6.0.2.) See here for changes: https://launchpad.net/python-mode/+announcements
Prolog-mode upgraded to 1.23. (Previous version was 1.19.) (Added support for XSB.)