A quick look at a Quick Look for Emacs from Charles Choi. MacOS has the notion of a Quick Look to peek at a file without invoking a heavier weight application such as an editor. It’s more than just dumping text onto the screen. It can deal with text, PDFs, HTML, various video files, ODF, Microsoft file types, and many others.
Choi likes the Quick Look functionality but, of course, would like to have it in Emacs too. It’s not clear how to do this in general but it’s trivially easy to do it for Dired and Ibuffer. Choi solves the problem by binding dired-display-file and ibuffer-visit-buffer-other-window-noselect to the Space key. These commands open the file in another window so they’re more than just open the file as usual in Emacs.
If you like the idea of being able to peek at a file without abandoning your current window, take a look at Choi’s post for the details on how to do it from Dired and Ibuffer windows.