Wolf-Extra is a mod for registered Wolfenstein, made by Poet. It was released on November 7, 1999.
Though the mod is no longer available and has not been available for quite some time, it still showcased some of the first mapping that Poet made; compact, difficult designs utilizing very little of the 64x64 slate all the while making for quite a challenging and imaginative gameplay.
Most of, if not all of the maps were inserted into Enemy Around the Corner, which is available in SDL. Tweaks were made to some of the maps, however.
In June 2019, Poet mentioned that he no longer had the original set at hand, and it is still quite sought after.
See also: Most wanted mods.