GROMACS

GROMACS is a very fast molecular dynamics code, which comes with lots of features like PME, a variety of cut-offs, non-equilibrium MD and more. The package includes also other algorithms like normal mode analysis and essential dynamics plus a wealth of analysis tools. It is supported by some of the leading trajectory viewers (VMD and gOpenMol). GROMACS is distributed under the GPL.
Find GROMACS at: http://www.gromacs.org