The commercial tools have made it easier for engineers at consultancies and utilities to build hydraulic models by integrating GIS and providing support for scenarios to compare different states of the model or future developments of a city.
Though as Tom points out, this comes at a huge price.
The US EPA does offer a simple GUI which can be used for smaller systems but without a connection to GIS, its usage has been limited.
These commercial versions have become enterprise monsters, they are very complex and expensive.
We wanted to create the right balance between what the US EPA already gives away for free and what the big vendors offer. We believe that releasing the software as FSL which transitions to MIT gives us the right head start and for the advanced features we're charging about 10% of what Autodesk and Bentley do - and for those that think that's too much, they of course can download and host their own private version too.
For those that are still curious, here are some extra links and context.
https://app.epanetjs.com/ – Try the app, it's local first and registration optional
https://github.com/epanet-js/epanet-js – Here is all the source code
https://github.com/epanet-js/epanet-js-toolkit – See how we converted the C engine to WASM
https://epanetjs.com/ – Read a landing page to see what we're doing and why, also our pricing
https://www.autodesk.com/products/infowater-pro/overview – Autodesk's product $10k/yr/user
https://en.virtuosity.com/openflows-water – Bentley's product $16k/yr/user