Linux
Convert RPM to CPIO archive for extraction
rpm2cpio package.rpm | cpio -dimv
Ubuntu: File-roller read RPM archives
Go to Synaptic and look for file-roller. Right-click it and see “suggested packages”. Install the RPM related packages from there, and file-roller will be able to open RPMs. This should be installed by default, in my opinion. It’s misleading to have .rpm files “associated” with file-roller when it can’t actually open them.