AmberTools21 is now available!
AmberTools consists of several independently developed packages that
work well by themselves, and with Amber20 itself. The suite can also be
used to carry out complete molecular dynamics simulations, with either
explicit water or generalized Born solvent models.
The AmberTools suite is free of charge, and its components are mostly
released under the GNU General Public License (GPL). A few components are
included that are in the public domain or which have other, open-source,
licenses. The sander program has the LGPL license.