Yes, I know it's not a square piano, but it's a compact and historically-interesting grand by the ever-inventive Robert Wornum.
This compact grand piano has a downstriking action, which enables the overall length to be kept small. The seller has provided a description in the attached document.
The seller has given us a link to a very enjoyable mini-recital on this beautiful instrument.
The price of this unusual instrument is €25,000. Please contact the owner: