geoShell Programmer's Development Package Manual by Maurice Randall, is designed to be an aid in developing commands for the GEOS geoShell program.  There are either three 1541 disks or a 1581 disk that accompanied this manual, but so far I've been unable to track down copies.  If you would like to share a copy, please use the Contact Us link in the banner.

Update - Bruce Thomas has tracked down the disk images, they can be found here.