The Strife Specibus fistkind is used by a few characters in Homestuck, most notably by Equius Zahhak. As the name suggests it involves the user attacking with their fists, though why one would need a strife specibus to wield their own fists is unclear.
Roxy Lalonde is also with a fistkind specibus in her Strife Portfolio, and she is seen using it during Collide. Her pre-scratch counterpart in was seen beating an enormous monster from LOLAR with only her fists as well.
So far, all users of this Specibus have been Void players. Void is the concept of nothingness, so this specibus could be see as "attacking with nothing."
Many players have been shown punching enemies and other players without Fistkind, so it can be assumed that this specibus amplifies the user's hand to hand ability.