There are many variants of the Kondo model. For instance, the spin-1/2 can be replaced by a spin-1 or even a greater spin. The two-channel Kondo model is a variant of the Kondo model which has the spin-1/2 coupled to two independent noninteracting bands. All these models have been solved by Bethe Ansatz. One can also consider the ferromagnetic Kondo model (i.e. the standard Kondo model with J > 0).