Faddensoft’s CiderPress received an update to v1.2.5. New to this version is the ability to convert to and from TrackStar 40-track “.APP” image files. This allows images created by the TrackStar system to be used in an Apple II emulator, and allows disk images created for use
in emulators to be used on a TrackStar board.
In addition, handling of mildly broken 2IMG images (with the ‘WOOF’ creator type) has been fixed.For anyone not familiar with the product: CiderPress is like a “ShrinkIt
for Windows” on steroids. It offers full access to ShrinkIt archives,
and allows you to view and extract files directly out of disk images, as
well as create ProDOS disk images. File converters translate programs,
documents, and graphics files into formats easily accessible under Windows
and other systems. Disk images can be converted between several different
formats. CiderPress costs $8.95.

Some more details about TrackStar “APP” images:

The TrackStar is a hardware Apple II emulator installed in a PC ISA slot.
They can occasionally be found for auction on eBay. Apple II 5.25?
drives can be attached to the board, allowing disks to be used directly.
The board also allows you to make file images of disks and boot from them
instead of physical disks.

The “.APP” images are in a variable-length nibble format, with a maximum
track length of 6525 bytes. The disks can be 40-track (encompassing the
standard 35 tracks used on the Apple II) or 80-track (a 40 track image
with the “half tracks” stored as well). Some common copy protection
formats, such as adding a 36th track or writing data in half-tracks,
are handled automatically.

The .APP format doesn’t convert well to or from the nibble-image format
common in the emulator world. “.NIB” images use fixed-length 6656-byte
tracks, which are longer than .APP supports. Converting from .NIB to .APP
requires removing an unused part of the track, and converting from .APP to
.NIB requires padding out one of the self-sync areas. These approaches are
unreliable on copy-protected disks, so the current version of CiderPress
doesn’t try to implement them.

Instead, all conversions to and from .APP files are done by interpreting
the source image as a formatted 16-sector disk. The new image is
constructed from the sectors.

Most disk images for emulators are already stored as sectors — .NIB
is fairly rare, because creating them is a relatively slow and awkward
process. Thus, the approach outlined above should be effective for
everything except 13-sector disks and copy-protected disks that would be
difficult to convert anyway.