MEMPAK is a static filesystem generator for volumes up to sixteen megabytes in size.
As of version 1.1z, it's available under the zlib license.

Volume Structure
$00 - $05 'MEMPAK' {$4D, $45, $4D, $50, $41, $4B}
$06 - $07 Number of Files (LO, HI)
$08 - ... Directory, each entry is in the following format...
$00 - $01 File Type (default is 'FX')
$02 - $04 Base Address (LO, MD, HI)
$05 - $07 Size (LO, MD, HI)
All pertinent file data is located after the directory.

Packing Options
-f infile.x Pull more arguments from infile.x
-e ex Set file type to 'ex' (default is 'FX').
-a sweep.csv Use amplitude sweep for 8-Bit DAC bias and step correction.
-b bittable Rearrange the bits in each byte (ex. '32107654').
-m bitmask Mask the bits of each byte (decimal, $hex, or %bin).
-r y/n Reverse the order of all file bytes (default is n/no).
Source data and options may be interleaved, for example...
mempak outfile.bin -b 01234567 source_a.bin -b 32107654 source_b.bin
...would yield a binary where the first file has the bits of each byte in reverse, but the second has the nibbles of each byte swapped.

Current Version
MEMPAK 1.1z 2016-8-9 Added : zlib license, file reverse (-r) option, support for Linux targets.

MEMPAK 1.0 2014-1-18 Initial Release

All content by Osman D. Celimli unless otherwise noted.
Not all of said content guaranteed to be useful. Some is probably quite old and dumb.
Oh my, here's a YouTube and Twitter.