There are a couple of utilities converting `polymake` file format from and to other formats used by various useful software packages. These collections is currently very small, but it grows by demand.

poly2leda_graph <file> <graph_section> { -directed, -undirected }
Convert a polymake graph into a leda graph, write the latter to standard output.
poly2lp <file>
Convert a polymake description of a polyhedron to LP format (as used by CPLEX and other linear problem solvers) and write it to standard output.
lp2poly IN_FILE.lp >OUT_FILE.poly
Convert a linear programming problem given in LP-Format (as used by cplex & Co.) to polymake description and print it to stdout.
porta2poly IN_FILE.{poi,ieq} >OUT_FILE.poly
Convert a polyhedron file in porta input format (.poi or .ieq) to polymake description and print it to stdout.