Diamond Computer Systems (later Diamond Multimedia) made some boards for IBM PC-compatible computers that were designed to foster Apple II interoperability. They could run Apple software on the built-in 6502 and ROM of the board; they had a BASIC that was written by The Learning Company and compatible with Apple Integer BASIC; Apple disks could be read from and written to in a PC disk drive, and optionally a Disk ][ for higher compatibility; and files could be accessed and transfered to and from the PC's filesystem.
Unfortunately, many of these boards are sold secondhand these days lacking documentation. So, I have made the documentation available here. Note that this is a scan of photocopied documentation, so it is readable, but it's not great.
You will need the DjVu viewer to make use of it.
Some files here: Trackstar Files
Mirrors here: Trackstar site mirrors