OS64 ROM Cartridge
Zebra Systems Inc.

This cartridge doubles the number of characters you can have on-screen on your TS2068 from 32 to 64.  

It puts the computer into one of its unusual hi-res modes and fixes all the issues caused by that; so (with a few oddities, explained in the manual) pretty much any BASIC program can be entered and will run as usual except with 64 characters across instead of the normal 32.  

This is not compatible with the regular (32-column) printer, you'll need a Centronics interface as well if you want to use LPRINT et al.