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.
UPXGui by: Dark Savant
UPXGui is a user made application, giving a more user friendly interface.
Copyright (c) 1996-2010 Markus Oberhumer,
Laszlo Molnar and John Reiser upx.sourceforge.net