Copyright © 2011 Massachusetts Institute of Technology
License: see zupolgec#1
edX published the same files here: https://github.com/edx/edx-platform/blob/master/common/lib/xmodule/xmodule/js/src/capa/schematic.js
This circuit simulator uses two js libraries: schematic.js for drawing circuits and cktsim.js for solving them.
The libraries have been written by MIT for the 6002x online course on the new MITx learning platform. I think they will be opensourcing all these libraries, and much more, soon.