EPA: Basins 4.0
"Installation software that contains the BASINS Version 4.0 system, data download tool, full documentation in the pulldown help menu, and the tutorial project and data (HUC-02060006) is now available. BASINS 4.0 contains the installation program for an open source GIS program (MapWindow ). At this time the only models available in BASINS 4.0 are WinHSPF and PLOAD and the tools GenScn and WDMUtil. BASINS 4.0 also contains a link to AQUATOX.
...GenScn is a model post processing and scenario analysis tool that is used to analyze output from HSPF and SWAT."