https://www.bamsoftware.com/software/exepack/
David Fifield <david@bamsoftware.com>

exepack is a compressor/decompressor for DOS executables in EXEPACK
format.

Compression:
	exepack unpacked.exe packed.exe
Decompression:
	exepack -d packed.exe unpacked.exe

It's written in Rust; you need rustc and cargo. To build:
	cargo build --release
The compiled program will be in target/release/exepack. There is
documentation in the doc and man directories.

To run the tests, do
	cargo test
The tests produce a bunch of valid and invalid EXE files; to save them
for investigation, run
	EXEPACK_TEST_SAVE_EXE=1 cargo test

An EXEPACK-packed file consists of compressed data, some metadata, and
an executable "stub" which, when run, decompresses the rest of the file
and jumps to the entry point of the decompressed executable. When
decompressing, this program understands several versions of EXEPACK (see
doc/README.stubs). When compressing, it tries to produce output that is
compatible, in terms of file offsets and metadata, with the format of
doc/stub_283.asm, which is the format documented at
http://www.shikadi.net/moddingwiki/Microsoft_EXEPACK#File_Format and
appears to be the most common. It however uses its own custom stub, one
designed to fix the bugs that are present in the other stubs.

If the program encounters an executable that resembles EXEPACK format
but which it can't handle, it will print out the contents of the EXEPACK
header and executable stub, and ask you to email them to the author so
that the format can be supported in the future.

This program only works with 16-bit DOS MZ executables. It does not work
with other formats that happen to have a ".exe" filename extension, such
as the PE (Portable Executable) format used for Windows executables, If
you try to compress a PE file, you will only end up compressing the DOS
stub (the short program that prints "This program cannot be run in DOS
mode", not to be confused with the EXEPACK stub).

Recommended alternative if this program doesn't suit your needs:
https://github.com/w4kfu/unEXEPACK