What does this mean? Extensible refers to Emacs being built upon a core set of routines hard-coded in C, which are then extended using a language called EmacsLisp. For this reason, Emacs remains the most powerful editor ever made - you can customize it to suit your needs perfectly. If there isn’t a feature, just add it! Emacs can do anything that can be coded in EmacsLisp, and that is a heck of a lot of things.
Here is a short list of Emacs features.
|Mark ring||Sort text||Math computation|
|Syntactic moves||Numbering||Emacs scripting|
|Search and replace||Spelling||Shell interface|
|Regexp handling||Templates||Session management|
|Keyboard macros||Abbreviations||Read mail and news|
|Highlight text||Tables||Browse man and info|
|Parenthesis match||File management||Online documentation|
|Rectangular selection||Programming modes||Chat|
|Registers, bookmarks||Version control||Draw ascii|
|Tags||FTP interaction||Play Tetris|
More reading on useful Emacs features:
Why choose Emacs over other editors: