We describe Nestor, a library to easily manipulate Fortran programs through a high level internal representation based on C++ classes. Nestor is a research tool that can be used to quickly implement source to source transformations. The input of the library is Fortran77, Fortran90, and HPF 2.0. Its current output supports the same languages plus some dialects such as Petit, OpenMP, CrayMP. Compared to SUIF 2.0 that is still announced, Nestor is less ambitious, but is light, ready to use, fully documented and is better suited for Fortran to Fortran transformations.