HSPF Toolkit for BMP Modeling Applications (EPA Ecosystems Research Division)

For model application in urban watersheds and areas with specific structural stormwater management measures (such as detention basins)

http://www.epa.gov/athens/research/modeling/ftable/index.htm

Data Master

Automation of data acquisition, measurement, and control systems. Accumulate, visualize, and analyze arrays of numeric data.

http://datamaster2000.tripod.com

REALM (REsource ALlocation Model)

Water supply system simulation package. System can be configured as a network of nodes and carriers representing reservoirs, demand centres, waterways, pipes, etc. Flexible "what if" tool to address various options (new operating rules, physical system modifications, etc)

http://www.dse.vic.gov.au/DSE/wcmn202.nsf/LinkView/4CE5EDD70A17665ACA257065001B60785CDA9AD32D09E6BDCA25706800060E85

CDM version of SWMM5

CDM makes available their version version of SWMM5 for download and use. There's a few more options and the GUI element edit boxes have a lot more variable options. Otherwise, it looks, feels, and acts like the EPA version (from what I've have discerned).

http://groups.google.com/group/swmm5

ReactOS (Windows XP alternative)

A free and open source alternative to Windows XP: ReactOS is a ground-up implementation of a Microsoft Windows XP compatible operating system.

http://www.reactos.org/en/index.html

BaseJumper

Rapid assessment tool for surface water and groundwater interaction: potential impact of groundwater pumping, land use change, etc have on the rate of change of baseflow contribution to streamflow.

http://www.skmconsulting.com/Markets/environmental/resource_management/BaseJumper.htm

TEDI

Impact of farm dams on streamflows at a catchment scale.

http://www.skmconsulting.com/Markets/environmental/resource_management/TEDI.htm

RORB Version 5

Runoff and streamflow routing program used to calculate flood hydrographs from rainfall and other channel inputs, applicable to both urban and rural catchments

http://www.skmconsulting.com/Markets/environmental/resource_management/RORB+Download.htm