> Conventional spreadsheets used on-screen cells to store all data, formulas, and notes. Improv separated these concepts and used the cells only for input and output data. Formulas, macros and other objects existed outside the cells, to simplify editing and reduce errors. Improv used named ranges for all formulas, as opposed to cell addresses.

Amazing.

Sounds very similar to how Coda works: https://coda.io

Quantrix Modeler is a successor of Improv. I personally love it, but pricing is quite steep.

Quantrix modeler is actually the successor to Quantrix for nextstep. Quantrix was a contemporary of Improv. Not sure I remember which came first. But Quantrix was the better of the two.

I'm collecting a pile of "good ideas"... Someday I'll do something with it.

The concepts are there in Microsoft's SSAS, which also lives in Excel as Power Pivot (only the Tabular engine, not the Multidimensional).

Almost any modern BI tool supports formulas; if you're interested exactly in n-dimensional data model try https://www.seektable.com

I was so happy to see someone mentioned improv before me :-)