trjconv (http://manual.gromacs.org/online/trjconv.html)
convert trajectory files in many ways
do_dssp (http://manual.gromacs.org/online/do_dssp.html)
do_dssp reads a trajectory file and computes the secondary structure for each time frame calling the dssp program.
g_correlation (http://www.mpibpc.mpg.de/grubmueller/g_correlation)
Generalized Correlation for Biomolecular Dynamics (g_correlation) allows to compute both, linear or non-linear genearlized correlation coefficients. The accurate characterization of correlated motions would also improve the interpretation of NMR experiments and X-ray diffusive scattering data.
g_rms (http://manual.gromacs.org/online/g_rms.html)
g_rms compares two structures by computing the root mean square deviation (RMSD)
g_rmsf (http://manual.gromacs.org/online/g_rmsf.html)
g_rmsf computes the root mean square fluctuation (RMSF, i.e. standard deviation) of atomic positions after (optionally) fitting to a reference frame.
g_sas (http://manual.gromacs.org/online/g_sas.html)
g_sas computes hydrophobic, hydrophilic and total solvent accessible surface area.
g_gyrate (http://manual.gromacs.org/online/g_gyrate.html)
g_gyrate computes the radius of gyration of a group of atoms and the radii of gyration about the x, y and z axes, as a function of time.
g_hbond (http://manual.gromacs.org/online/g_hbond.html)
g_hbond computes and analyzes hydrogen bonds.
g_dist (http://manual.gromacs.org/online/g_dist.html)
g_dist can calculate the distance between the centers of mass of two groups of atoms as a function of time.
g_energy (http://manual.gromacs.org/online/g_energy.html)
g_energy extracts energy components or distance restraint data from an energy file.
g_rama (http://manual.gromacs.org/online/g_rama.html)
g_rama selects the Phi/Psi dihedral combinations from your topology file and computes these as a function of time.
g_covar (http://manual.gromacs.org/online/g_covar.html)
g_covar calculates and diagonalizes the (mass-weighted) covariance matrix.
g_cluster (http://manual.gromacs.org/online/g_cluster.html)
g_cluster can cluster structures with several different methods.