InlandECDIS is a standard for chart plotters on European (basicly) Inland waterways. Equipment mandatory for commercial boats and barges in those waters.
There are few equipment manufacturers and OpenCPN made an effort some years ago to add the required functionalities to cover the standard. Next we did an auto-certificate of compliance, which is required for the user in order to be legal.
You will find mainly two types of users and skippers on the waterways: Large companies with bigger fleets and hired staff and families running their barge. The latter have a very small margin to survive. This is one reason why InlandENCs are free. They just can’t afford them. OpenCPN fits in that niche.