Bentley WaterGEMS

Free, public-domain stormwater, wastewater, and combined sewer system simulation model by the US Environmental Protection Agency -- dynamic hydrology-hydraulic-water quality simulation for single-event or continuous modeling of rainfall-runoff, pipe/channel routing, green infrastructure/LID controls, and pollutant loads; the industry-standard computational engine used worldwide for drainage design, CSO/SSO mitigation, floodplain mapping, and regulatory compliance (NPDES, CMOM, TMDL).

Free, public-domain water distribution system modeling software by the US Environmental Protection Agency -- performs extended-period simulation of hydraulic and water-quality behavior within pressurized pipe networks (pipes, pumps, valves, tanks), tracking flow, pressure, water age, chlorine residuals, and contaminant transport; provides a C Programmer's Toolkit (DLL with 50+ functions) for custom integration; the industry-standard computational engine underlying most commercial water-distribution modeling packages worldwide.

Integrated catchment modeling software for stormwater, wastewater, and flood network analysis -- 1D/2D hydraulic and hydrologic simulation, cloud or local compute, collaborative scenario management, and rule-based network design for sewer and stormwater engineers at utilities and engineering consultancies.

Hydraulic transient and surge-analysis software for water distribution and wastewater piping systems. Bentley now licenses HAMMER through the OpenFlows Water family, where the current Standard, Advanced, and Ultimate tiers include the named HAMMER transient-analysis capability.