FVWM (1993) is (among) the oldest [Li|U]nix window managers still in active use, development, and deployed enjoyment. Numberless window managers — notably, Afterstep, Enlightenment, Metisse, and Xfce — are FVWM forks by ancestry (or guilty intent).
For your halcyon delight, Raiazome has developed a resource-efficient, wallpaper-, keyboard-, and console-centric recipe (i.e., skinned theme) for FVWM — named Arlun, after the Welsh for “painting.” See:
FVWM is noted for ‘extreme’ configurability and that, once configured, its chameleon-like carapace of dialogs, icons, menus, and panels can be conjured into mimicing (most) any other 2D window manager.
FVWM is also noted for its scripting language (which, enjoined to no specific name, is named the “FVWM Language”). This language bears incidental resemblence to the Emacs-specific scripting language, Emacs Lisp, in that — as Emacs is configured through and third-party “modes” coded in Emacs Lisp — FVWM is configured through and third-party “themes” coded in the FVWM Language.
This language, being somewhat full-fledged, supports the full array of scripting necessities: scalar variables, list variables, procedural functions, shell contexts, and so on. And, being the heated core at the heart of FVWM‘s well-noted configurability, this language provides access to all aspects, dynamic and static, of window manager context, windowing session, and windows for the currently running FVWM process.
This language has been reified, recently, in the shiny clutches of a “new” window manager, referred to as:
It’s not unreasonable, therefore, to speak of the FVWM Language as the world’s first (and, still, most widely used) “window manager-specific language.”
FVWM, aside the like of commoner, everyday window managers like KDE, GNOME, and ratpoison, is denigrated as a has-been, seen-better-decades window manager. Nevertheless, given its recent reconception in the translucid, crystalline lids of FVWM-Crystal, the over-spoken tides of its death may yet be turned aside.