The TI-99 was a deeply weird microcomputer from 1981, whose main claim to fame was being built around a 16-bit TMS9900 CPU --- and also having only 256 bytes of system RAM, with an additional 16kB of video RAM, requiring the BASIC to store the user's program in video RAM.
It had an optional rack-mount expansion system with an optional disk drive. This was controlled by a standard FD1771 or FD179x chip, meaning a relatively normal IBM-scheme disk format of 35 tracks containing nine 256-byte sectors.
FluxEngine can read these.
(no options)
To read:
fluxengine read -c ti99 -s drive:0 -o ti99.img