The mscompress package contains two programs: msexpand, which decompress files compressed by the Microsoft compress.exe utility (e.g. Win 3.x installation files) and mscompress, which compresses files using the LZ77 compression algorithm. Output files can be decompressed using Microsoft expand.exe or msexpand.
MPIBZIP2 is a parallel implementation of the bzip2 block-sorting file compressor that uses MPI and achieves significant speedup on cluster machines. The output of this version is fully compatible with bzip2 1.0.2 or newer (i.e. anything compressed with MPIBZIP2 can be decompressed with bzip2).
open-vcdiff contains an encoder and decoder for the format described in RFC 3284: "The VCDIFF Generic Differencing and Compression Data Format." Given a source file and target file, the encoder produces a compact delta file expressing the differences between the two. The decoder reconstructs the target file from the source and delta files. The package includes libraries, headers, and a command-line executable. The chief reason for developers to use open-vcdiff instead of the existing Xdelta package is that open-vcdiff has been released under the Apache license rather than GPL.
BZip2/OSS-QM is the OSS-QM project's branch of bzip2, which contains a lot of fixes not yet in the original upstream. The primary goal is to provide QM'ed/fixed versions of upstream releases, so they can be built and used without additional patches, especially in sysrooted crosscompiling environments.
Multicrush is a wrapper around pngcrush that distributes the work of brute-force compressing a single image over several pngcrush processes. This gets you a slightly less than a linear speedup, caused by different compression methods having slightly different durations. For example, the author has measured a speedup of 1.92 on a 2-core Intel T5300, and 3.86 on a 4-core Intel Q6600. The only requirements are a copy of pngcrush and at least Python 2.4. If you have version 2.6 or higher, multicrush can automatically detect how many CPUs to use.