Quantrix isn't quite mainstream, but is very similar to Improv.
I know about it, but I'm guessing it's quite expensive. The certainly make it difficult to figure out pricing (or even just get the trial).
There are a couple of recorded webcasts where they mentioned the pricing; it's approximately $2k/seat/year, if I recall correctly. They do make you register for the trial, but they approve it quickly. It's definitely worth checking out.
Thanks for the info. It's a bit expensive for me. I've been wondering about a good long term project and this might be it. I'll have to think about it.
What specifically do you miss about it?
It's hard to say. It's very much like a spreadsheet, but has additional features. One of the ideas from it is now in Excel as pivot tables, but it's done much better in Improv.