TI IBM Connection allows you to move text files from TI formatted disks to IBM PC formatted disks on your TI. It requires two things to work: a CorComp DSDD controller (either the one for the PEB or the 9900 Micro Expansion System) and two disk drives (preferably 360K). It may work with the Atronic or BwG disk controllers, as most software detects them as CorComp controllers, even though they are not. It will not work with Myarc, TI, or Percom Data disk controllers.
Navarone Disk Fixer is a sector editor program for your TI. It allows you to look at and modify the contents of sectors on the disk--and is a really easy way to destroy a disk if you don't know what you are changing. Hunt down a copy of the book: The Hidden Powers of Disk Fixer by Bill Gronos for a really nice manual for this cartridge. It may be on WHTech, but I haven't looked for it specifically there.
Of the two, TI/IBM Connection is seen much less often than Disk Fixer (by about ten to one--I have seen at least 10 listings for Disk Fixer over the years, and only one TI/IBM cartridge). I have both of these cartridges (I bought the TI/IBM when it first came out, and Disk fixer slightly later).