Archives is an unarchiving app for your iPhone or iPad that can open pretty much any archive file in existence. It is based on the extremely popular macOS app "The Unarchiver".
It can open files that have been mailed to you, files you encounter on the web, or even files from your computer through iTunes file sharing. It lets you preview the files inside archives, such as text, images or music. If you have another app installed that can open a file, Archives can also use that app to open contained files.
As it is based on The Unarchiver, it can handle a large number of different archive formats: Common formats like Zip, RAR, 7-zip, Tar, Gzip and Bzip2, as well as older formats like StuffIt, DiskDoubler, LZH, ARJ and ARC. It can also handle other kinds of formats, like CD and DVD images such as ISO, BIN, MDF, NRG and CDI, many Windows self-extracting EXE files, and can even extract media from Flash SWF files and images from PDF files. See the Archives web page for a full list.