It replaces the text editor of previous Macintosh operating systems, SimpleText. TextEdit reads and writes documents in Rich Text Format as well as ASCII and HTML, can open (but not edit) old SimpleText files. It also has access to the operating system's built-in spell-checking service. The version included in Mac OS X 10.3 Panther added the ability to read and write documents in Microsoft Word format.
Mac OS X, as a Unix-based operating system also includes emacs, vi and pico as well as other terminal-based text editors.