 Classic programs include the Electric Power Research Institute's (EPRI) CAFTA software, which is used by many of the US nuclear power plants and by a majority of US and international aerospace manufacturers, and the Idaho National Laboratory's SAPHIRE, which is used by the U.S. Government to evaluate the safety and reliability of nuclear reactors, the Space Shuttle, and the International Space Station.Outside the US, the software RiskSpectrum is a popular tool for fault tree and event tree analysis, and is licensed for use at almost half of the world's nuclear power plants for probabilistic safety assessment.Professional-grade free software is also widely available; SCRAM is an open-source tool that implements the Open-PSA Model Exchange Format open standard for probabilistic safety assessment applications.