Quadratic algebra of square groups
  There is a long-standing problem of algebra to extend the symmetric monoidal structure of abelian groups, given by the tensor product, to a non abelian setting. In this paper we show that such an extension is possible. Morover our non abelian tensor product remains even right exact and balanced. We describe the new non-abelian tensor product in the context of quadratic algebra which extends linear algebra. 
H.-J. Baues, M. Jibladze, T. Pirashvili