K0 of purely infinite simple regular rings

We extend the notion of a purely infinite simple C*-algebra to the context of unital rings, and we study its basic properties, specially those related to K-theory. For instance, if R is a purely infinite simple ring, then K-0(R)(+) = K-0(R), the monoid of isomorphism classes of finitely generated projective R-modules is isomorphic to the monoid obtained from K-0(R) by adjoining a new zero element, and K-1(R) is the Abelianization of the group of units of R. We develop techniques of construction, obtaining new examples in this class in the case of von Neumann regular rings, and we compute the Grothendieck groups of these examples. In particular, we prove that every countable Abelian group is isomorphic to K-0 of some purely infinite simple regular ring. Finally, some known examples are analyzed within this framework.