I would like to have Jmol read GROMACS output file format, .gro
The GROMACS file format family was created for use with the molecular simulation software package GROMACS. It closely resembles the PDB format but was designed for storing output from molecular dynamics simulations, so it allows for additional numerical precision and optionally retains information about particle velocity as well as position at a given point in the simulation trajectory. It does not allow for the storage of connectivity information, which in GROMACS is obtained from separate molecule and system topology files. The typical file extension for a GROMACS file is .gro.
I am attaching some example files taken from the examplees in GROMACS installation (a peptide, a box of water molecules, a box of urea in water) and, for reference, the equivalent pdb files obtained using the Gromacs converter program, "editconf".