FiscalSim US is an open source microsimulation model of the US federal and state household tax and benefit system. It is supported and maintained by The Center for Growth and Opportunity at Utah State University (CGO). Much of the original federal tax and benefit code and some of the state tax logic was developed by PolicyEngine, with which CGO originally had a partnership. Their US model is at https://github.com/PolicyEngine/policyengine-us.