C++QED is a highly flexible framework for simulating open quantum dynamics, which I have developed since 2006. It allows users to build arbitrarily complex systems from elementary free subsystems and interactions, and simulate their time evolution with a number of available time-evolution drivers.
More on the project website
Some notes in physics
These are things that one tends to come across as a physicist, often in some not satisfactorily articulated form. Here they get articulated.