The aim of the DIET project is to develop a set of tools to build computational servers. Huge problems can now be computed over the Internet thanks to Grid Computing Environments like Globus or Legion. Because most of current applications are numerical, the use of libraries like BLAS, LAPACK, ScaLAPACK or PETSc is mandatory. The integration of such libraries in high level applications using languages like Fortran or C is far from being easy. Moreover, the computational power and memory needs of such applications may of course not be available on every workstation. Thus, the RPC seems to be a good candidate to build Problem Solving Environments on the Grid. Several tools following this approach exist, like Netsolve, NINF, NEOS, or RCS.