Oh, for sure-- Its an RS232 hosted block device provider. Just about any PC compatible with a serial port should be supported.
The PCjr is a noteworthy target, because it never really had an official hard disk solution produced for it. Racore inc produced the Drive II topper expansion that brought the system up to its maximum of 512kb (Due to the afore mentioned odd memory map, and where the "Not EGA" card's graphics memory starts, this is the tops) while adding a second diskette drive, and the vintage computer enthusiast community produced a homebrew sidecar called the Jr IDE that provides an 8bit IDE interface with XT-IDE bios to get hard disk capability, but an unmodified system is very resource constrained indeed.
Its resource constrained-ness is a significant factor in why JrIDE was developed. (It also provides RAM to reach the maximum 512k on systems without the racore expansion). Early efforts to get something "Hard disk like", included using an iomega zip100 parallel port drive on it, with many numerous issues with the driver being too large for the Jr's very minimal memory compliment.
Fujinet here is a very impressive accomplishment, running on an unmodified Jr in this way.
Just saying, its actual usefulness there is rather limited. 😀
More mileage would be gotten from some other system. If it actually had the needed ports, an IBM PC Portable would be a more forlorn device to pair it on, since it's LCD was actually fully software compatible with CGA graphics modes. (Just squashed, and monochrome.) Sadly, IBM did not include an RS232 port on it. (Though it does have a built in ISA slot header in its expansion area... which is too small for a real ISA card. A custom PCB might fit there though.)