Cool project for sure, but it does provoke the obligatory Emacs org-mode as a spreadsheet plug. 
I use it often, mostly for my D&D character sheet, but occasionally for work.
Works the same in terminal or GUI, with elisp formula evaluation (including Emacs calc functions), column types, table relationships, and, with org-babel, access to other languages and their libraries (for plotting, etc.) Can even read from DB into an org table and then manipulate data and write back.
At first glance, it seems like Lisp is inappropriate for spreadsheets: the syntax is simply too verbose and heavy. But cool project, I've always wanted to make a terminal spreadsheet app. Maybe with some custom APL-like language. Now that would be cool!
I fully agree with you. When you see how cumbersome Excel formulas can be when you want to mix different operators together, with their "(",";" and so on and so forth. I wonder how you can say that Lisp is too verbose for this task.
Furthermore, this spreadsheet is fully "libre", you can modify it and transform it according to your needs.
There is also the possibility to write "regular formulas", which are more similar to what people are used to.
Seems interesting. I was curious about how mouse support was retrofitted into the app but discovered that the commit messages are unfortunately absolutely useless for seeing recent changes. They’re all “update xxx.cpp” or just “bug” [sic].
please accept my apologies, I should be more verbose in my comments. The whole implementation is in tamgusys.cxx. See inmouse and outmouse for more details. Basically, inmouse activates the mouse catching events, which are sent through getchar. Once, the mouse has been activated, you can use some primitives mouedown1 our mouseup, which takes as input the string returned by getchar and returns the x,y coordinates
Interesting. On a somewhat related note, I wonder how much work it would be to port scheme in a grid to racket, or somehow get it working on modern distros/os' (it's been abandoned for a while, and uses a ui toolkit that's been abandoned too):