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In that space, https://blockpad.net/ is interesting also

Which is your industry, if you don't mind me asking?

Civil engineering

Oh, I miss MathCad, I wish we had a decent FOSS clone.

I find Julia’s Pluto to be reasonably close alternative.

Of course it lacks many features, but plugins systems and overall architecture gives hope for possible extension to include many of the desired features.

Wait, Mathcad is unmaintained? What happened?

It became Mathcad Prime that is still maintained and had a release this year.