CotEditor

CotEditor is a lightweight plain‑text editor built exclusively for macOS, offering a native look and feel that matches the platform’s conventions. It launches quickly, allowing users to begin typing without delay, and runs as an open‑source project that can be freely contributed to and modified.

The editor supports syntax highlighting for more than sixty common languages, such as HTML, Python, Ruby, and Markdown, with the ability to add custom definitions. It includes a powerful find‑and‑replace feature powered by the ICU regular‑expression engine, automatic backups of unsaved work, and an outline menu that extracts and navigates predefined syntax lines. Users can split the window into multiple panes, inspect Unicode character details, and check for characters incompatible with a chosen encoding.

CotEditor also provides scriptability, enabling macros written in languages like Python, Ruby, Perl, PHP, shell scripts, AppleScript, or JavaScript. It handles CJK text accurately, supporting vertical text mode and proper line‑height rendering, making it suitable for developers and writers who need a fast, extensible, and macOS‑centric plain‑text editing experience.