Shapestack is a 1K ZX81 puzzle game I originally wrote 25 years ago.
This version is a bugfix release, but I also took the opportunity to
adopt the name used in Cronosoft's "1K Games Pack #1" release from
2011.
From day one, pressing Shift would crash the game - this version fixes
that. It's also seven bytes smaller, because why not.
The web page is here:
https://zgedneil.nfshost.com/shapestack.html
-Rus.