  Here we present a program aimed at free-energy calculations in molecular
systems. It consists of a series of routines that can be interfaced with the
most popular classical molecular dynamics (MD) codes through a simple patching
procedure. This leaves the possibility for the user to exploit many different
MD engines depending on the system simulated and on the computational resources
available. Free-energy calculations can be performed as a function of many
collective variables, with a particular focus on biological problems, and using
state-of-the-art methods such as metadynamics, umbrella sampling and
Jarzynski-equation based steered MD. The present software, written in ANSI-C
language, can be easily interfaced with both fortran and C/C++ codes.
