1. Integer and Nonlinear Optimization in R - The project "Integer and Nonlinear Optimization in R (RINO)" provides the packages Rbonmin, Rlago (both interfaces to MINP solvers) and solnp.
4. R/GNU Linear Programming Kit Interface - GLPK is an open source software for solving large-scale linear programming (LP), mixed integer linear programming (MILP) and other related problems. Rglpk provides a high level interface to R for solving LP/MILP problems.