syntax highlighting: colorize more than 50 preinstalled major languages like html, php, python, ruby or markdown. you can also create your own settings.
scriptable: make your own macro in your favorite language, whether it is python, ruby, perl, php, unix shell, applescript or javascript.
outline menu: extract specified lines with the predefined syntax, and you can jump to the corresponding line.
powerful find & replace: super powerful find and replace using the icu regular expression engine.
split editor: split a window into multiple panes to see different parts of your document at the same time.
incompatible characters: check and listup the characters in your document that cannot convert into the desired encoding.
cjk language friendly: estimate various file encodings accurately, toggle to vertical text mode and keep its line height correctly.
open source: coteditor is developed as an opensource project that allows anyone to contribute. (github https://github.com/coteditor/coteditor )