WaterBase is a set of tools from the United Nations University for applying the SWAT model from USDA-ARS: "SWAT is a river basin scale model developed to quantify the impact of land management practices in large, complex watersheds."
MWSWAT: MapWindow/SWAT interface tool
SWATPlot: SWAT visualisation tool
SWATGraph: SWAT visualisation tool
MWAGNPS: MapWindow/AGNPS interface tool