I bought an XL on ebay that included a cart which I don't think has been dumped before. It's a message display program (and frankly, not a very good one.) I found the man who created the cart and interviewed him (the interview will run on the ANTIC podcast.) Apparently this was intended for use to display messages to patrons in places like bowling alleys. Only about 20 were sold.
Tonight Sal Esquivel showed me how to dump it. The binary is attached (standard 8K cart), plus some pictures of the computer and the cart.
Wilcox Message Display.bin 8KB 125 downloads