A free, portable, extendable, high-performance for several executable formats.
BSEditor: UPX achieves an excellent compression ratio and offers very fast decompression. Your executables suffer no memory overhead or other drawbacks for most of the formats supported, because of in-place decompression. UPX strengths in a Nutshell:

* excellent compression ratio: typically compresses better than WinZip/zip/gzip, use UPX to decrease the size of your distribution!
* very fast decompression: ~10 MB/sec on an ancient Pentium 133, ~200 MB/sec on an Athlon XP 2000+.
* no memory overhead for your compressed executables because of in-place decompression.
* safe: you can list, test and unpack your executables. Also, a checksum of both the compressed and uncompressed file is maintained internally.
* universal: UPX can pack a number of executable formats.
* portable: UPX is written in portable endian-neutral C++.
* extendable: because of the class Layout Its very easy to add new executable formats or new compression algorithms.
* free: UPX is distributed with full source code under the GNU General Public License v2+, with special exceptions granting the free usage for commercial programs as stated in the UPX License Agreement.

News

08 Sep 2010: UPX 3.07 has been released. It is a minor 3.0x maintenance release to version 3 whose major additions were:

* optional LZMA compression
* support for BSD systems you can free download UPX 3.07 now.