22DISK is a shareware tool for reading/writing CP/M disks under MS-DOS, or Win 9x (only in a full-screen DOS box, <Alt>-<Enter>.)
You can download it from
http://www.cpm.z80.de/download/22dsk142.zip
Native support is only for HP 86, 87, 125 - DSDD 48 tpi 5.25" floppy disk (HP1 diskette type).
The files I got from Stephen allow to extend the support to HP 86, 87, 125 - SSDD 48 tpi 3.5" floppy disk (HP2 diskette type).
There is a special HP CP/M boot disk that contains 3 files: Autost, CP/M, and CP/MSYS.
CP/MSYS is a large file on the disk that contains the CP/M file system and the basic files normally expected in a bare bones CP/M system.
Apparently the HP is using the CP/MSYS file as an IMG file, such as linux does, allowing a file to be attached as a device and accessed as a drive.
So, yes, with a tool like 22DISK, extended, you can access that IMG file, and list, delete, copy from/to DOS any text of binary CP/M-80 file.
I was able to copy and execute programs like Mbasic (Microsoft Basic), TP 1.0 (Turbo Pascal), MP (Multiplan) and others, downloaded from any site that has CP/M-80 programs.
Of course, maybe, there are some limitations, but I could't find any for now.
Not sure about graphics CP/M-80 programs. I didn't test that feature yet.
As you said, that hugely increase the amount of CP/M software for the HP 86/87...
I think that CP/M for the HP 86/87 was underestimate until now.
Btw, let me know if you need a copy of the CP/M boot disk rev B 3.5" in TD0 format, as on the hpmuseum.net there is only the 5.25" format to download.
Have fun with CP/M for the HP 86/87.