Kel-Tec has long been renown as the most innovative (but not necessarily good) manufacturer of firearms. This prototype was designed during the 1994 AW ban, that’s why it has a oddly cut barrel.

This novel barrel is for a mounting system that could attach muzzle devices without having a ‘threaded barrel’, which might have prohibited it legally.

The lower receiver and the trigger of this prototype rifle look to be 3D printed whereas the upper receiver cover is probably made of some sort of thermoplastic material like Kydex. The charging handle is located above the lower receiver and below the barrel. It is probably an ambidextrous or reversible one. The barrel looks to be fixed in place via a barrel nut. You can see the threaded portion of the barrel and the nut screwed on it right in the front of the lower receiver and Picatinny rail base.

https://www.thefirearmblog.com/blog/2018/04/06/kel-tec-prototype-308-bullpup-rifle/