GNU Emacs

https://www.gnu.org/software/emacs/

Emacs and its derivatives are a family of text editors that are characterized by their extensibility. The manual for the most widely used variant, GNU Emacs, describes it as "the extensible, customizable, self-documenting, real-time display editor". Development of the first Emacs began in the mid-1970s and continues actively as of 2015. Emacs has over 2,000 built-in commands and allows the user to combine these commands into macros to automate work. Emacs Lisp provides a deep extension capability allowing users and developers to write new commands using a dialect of the Lisp programming language.