UPX is a free, portable, extendable, high-performance executable packer for several different executable formats. It achieves an excellent compression ratio and offers very fast decompression. Your executables suffer no memory overhead or other drawbacks because of in-place decompression.

What's New in version 3.04:

• new format Mach/AMD64 supports 64-bit programs on Apple Macintosh.
• new formats Dylib/i386 and Dylib/ppc32 support shared libraries [such as browser plugins] on Darwin (Apple Macintosh). An existing -init function (LC_ROUTINES command) is required.
• new format vmlinuz/armel for Debian NSLU2 (etc.) linux kernel
• bvmlinuz boot protocol 2.08 for 386 Linux kernel
• Extended ABI version 4 for armel-eabi ARM Linux ELF
• bug fixes