On Amiga platforms there are programs called "lha" and "lzx" - enough for 95% of files stored on Aminet. Zip files and rar files can be un-packed by using "unzip" or "unrar" programs. All these programs must be launched from shell. There are un-packing programs with GUI, but it's another story. AOS3.9 is equipped with GUI un-packer already.
Under Windows:
Use WinRAR - the best choice.
