Emacs

GNU Emacs is a text editor whose behaviour is written almost entirely in its own Lisp dialect and can be redefined while it is running. Any key, command or display rule is changeable without rebuilding the program, and every function and variable carries documentation the editor will show you on the spot — the reason it is called self-documenting.

Because editing behaviour is decided by major and minor modes, Emacs covers a great deal beyond programming: Org mode for outlines, notes, tasks and documents that mix prose with code; Dired for file management; shells and a terminal emulator running inside a buffer; version control; mail and news readers. A package manager installs further extensions from GNU ELPA and other archives.

This entry is the Android build, which runs the same C core and the same Lisp code as the desktop version, so an existing configuration and installed packages largely carry over. Emacs leans heavily on Control and Meta key combinations, which are awkward on a touch keyboard, so it is considerably more comfortable with a physical keyboard attached.