JSIM and the noise-enabled JSIM_n are ubiquitous Josephson circuit simulators; faster than Spice with inherent support for the Josephson junction.

The source code with makefile is included as a tar.gz archive, and is easy to build on Linux and Mac platforms.

The original paper on JSIM is also included because it is very difficult to find. It should be referenced as: E. S. Fang and T. Van Duzer, "A Josephson integrated circuit simulator (JSIM) for superconductive electronics application," in Extended Abstracts of 1989 Intl. Superconductivity Electronics Conf. (ISEC '89), Tokyo, Japan: JSAP, 1989, pp. 407-410.