Paul Feautrier is the main developer of Pip (Parametric Integer Programming) since its inception in 1988. Basically, Pip is an ``all integer'' implementation of the Simplex, augmented for solving integer programming problems (the Gomory cuts method), which also accepts parameters in the non-homogeneous term. Most of the recent work on Pip has been devoted to solving integer overflow problems by using better algorithms. This has culminated in the implementation of an exact arithmetic version over the gmp library.
Pip is freely available under the gpl at http://www.prism.uvsq.fr/~cedb/bastools/piplib.html . Pip is widely used in the automatic parallelization community for testing dependences, scheduling, several kind of optimizations, code generation, and others. Beside being used in several parallelizing compilers, Pip has found applications in some unconnected domains, as for instance in the search for optimal polynomial approximations of elementary functions (see the Inria project Arénaire).