I suppose it's correct to say EPANET competes with expensive commercial offerings, but it's actually available completely free:

https://www.epa.gov/water-research/epanet

I know someone who uses it to design clean drinking water distribution systems in rural communities in Central America. They would not be able to do what they do if they had to pay for an expensive commercial licence.

Desktop EPANET is still windows-only though, so having a browser version is pretty cool.