Smart Key - Treemacs

Treemacs is an add-on Emacs package that offers a fixed, per-frame, graphical window for hierarchically browsing and operating upon directories, files and programming tags within files. Use the Emacs package manager to install it and then invoke it with {M-x treemacs RET} and quit with {q}.

Treemacs items may be dragged with the Action Key to other windows for display. See Displaying Items.

When in a Treemacs file browser buffer:
  ACTION KEY or ASSIST KEY
     (1) on or to the left of an entry icon, run the treemacs TAB command
         to expand or collapse the entry;
     (2) elsewhere within an entry line, display the item, which may be a
         directory, for editing, normally in another window;
     (3) at the end of an entry line: if an Action Key press, invoke
         action-key-eol-function, typically to scroll up proportionally;
         if an Assist Key press, invoke assist-key-eol-function, typically
         to scroll down proportionally;
     (4) at the end of the first or last line of the buffer, quit this
         Treemacs invocation.