What is the Ubuntu archive manager?

The package name is file-roller. This was discovered using apt-cache search "archive manager".

From the docs:

Description-en: archive manager for GNOME
 File-roller is an archive manager for the GNOME environment. It allows you to:
 .
  * Create and modify archives.
  * View the content of an archive.
  * View a file contained in an archive.
  * Extract files from the archive.
 .
 File-roller supports the following formats:
  * Tar (.tar) archives, including those compressed with
    gzip (.tar.gz, .tgz), bzip (.tar.bz, .tbz), bzip2 (.tar.bz2, .tbz2),
    compress (.tar.Z, .taz), lzip (.tar.lz, .tlz), lzop (.tar.lzo, .tzo),
    lzma (.tar.lzma) and xz (.tar.xz)
  * Zip archives (.zip)
  * Jar archives (.jar, .ear, .war)
  * 7z archives (.7z)
  * iso9660 CD images (.iso)
  * Lha archives (.lzh)
  * Single files compressed with gzip (.gz), bzip (.bz), bzip2 (.bz2),
    compress (.Z), lzip (.lz), lzop (.lzo), lzma (.lzma) and xz (.xz)
 .
 File-roller doesn't perform archive operations by itself, but relies on
 standard tools for this.
Homepage: http://fileroller.sourceforge.net/

It is an application to manage/extract/create archives like: .tar, .gz, .zip, etc.

More about: https://apps.ubuntu.com/cat/applications/file-roller/.