The Biaxe guitar was invented around 1976 by Charles Churchman Soupios as dual-necked instrument for touch-style playing. You were meant to play each neck with a different hand - one being the bass neck and the other the treble. The design was patented in 1981 and the company made them from around 1978 to 1985. Charles Soupios returned in the 1990s with a detachable neck Biaxe invention - whereby an additional neck could be fitted to a standard guitar making it into a Biaxe.

Source: Biaxe patent #US4240319A granted 23 December 1981

Source: Detachable neck Biaxe patent #US5315910A granted 31 May 1994

Source: Biaxe video - Chuck Soupios 1985