Editable software

How awesome is it that if some functionality doesn't exist in Emacs, you can just add it in with your own function. (And usually you don't have to write it yourself - a quick search will find that someone else has done it already.)

e.g., I wanted a way to remove a link in org-mode, but leave the description. (Kind of surprised that isn't built-in to be honest, but there we go). The Emacs StackExchange has a bunch of ways of doing that.