Charm++ is a message-passing parallel language and runtime system.
It is implemented as a set of libraries for C++, is efficient,
and is portable to a wide variety of parallel machines.
Source code is provided, and non-commercial use is free.

Charm++ is developed in the University of Illinois, and is
used primarily by the NAMD, the molecular simulation system.

WWW: https://www.ks.uiuc.edu/Research/namd/