.HQX files are BinHex, and most archive/dearchive utilities can handle them. BinHex is a text file format converting BINary to HEXadecimal, making it easier to send a file via email and chop into chunks, and often decodes into another archive format like .SIT, .CPT or .ZIP. In some versions of Stuffit, there's preferences to let you continue unarchiving the file once you get it un-BinHexed, and optionally get rid of the BinHex files once they're decoded since BinHexed files end up being larger than the original archive file.