Instantons on Quivers and Orientifolds
  We compute the prepotential for gauge theories descending from ${\cal N}=4$ SYM via quiver projections and mass deformations.   This accounts for gauge theories with product gauge groups and bifundamental matter. The case of massive orientifold gauge theories with gauge group SO/Sp is also described. In the case with no gravitational corrections the results are shown to be in agreement with Seiberg-Witten analysis and previous results in the literature. 
Francesco Fucito, Jose F. Morales and Rubik Poghossian