CotEditor - Open Source Plain-Text Editor for OS X
Notepad++ - A free source code editor which supports several programming languages running under the MS Windows environment.
Sublime Text - Sublime Text is a sophisticated text editor for code, html and prose - any kind of text file. You'll love the slick user interface and extraordinary features. Fully customizable with macros, and syntax highlighting for most major languages.
Gobby - Collaborative text editor with syntax highlighting that lets you work with a team on the same...
BBEdit - BBEdit is a professional HTML and text editor for Macintosh that provides features for editing, searching, and minipulation of text for web authors and software developers.
Notion - All-in-one workspace. One tool for your whole team. Write, plan, and get organized.