Commercial application to compress or decompress files (ZIP, LHA, ARC, RAR, LZH, UU, TAR, TGZ, etc). See http://www.rarlabs.com
WinRAR is a powerful archive software. It can backup your data, reduce size of email attachments and other files. It is distributed by http://www.rarlab.com/ A great windows based archive utility, powerfull replacement of WinZip