Quantrix is still popular today for large financial modelling. The main advantage of Improv/Quantrix was that everything is named, and formulas are expressed as logical formulas, not references to spreadsheet columns, which makes the spreadsheets themselves more interpretable and readily auditable. If you're disciplined with named ranges, you can do a similar thing in Excel these days, but it doesn't really feel as natural as it did in Improv, and on a multi-person team with varying Excel skill levels it can be a challenge to maintain that discipline.