rpmcommand to install software in RPM format because Debian uses its own package management called DPKG.
But there is an experimental software called Alien, that converts between the RPM, Debian DEB, Stampede SLP, and Slackware TGZ file formats.
For example, if you want to install Inkscape which is in a binary RPM format, in Ubuntu (or any Debian based Linux distribution), you can use the following command:
# alien -i inkscape-2.1.3.rpm
This will unpack the RPM package into a directory, create a DEB package and then install it on your system. Of course, you can uninstall the package at a later date by using the relevant DPKG command.
Alien should not be used to replace important system packages, like sysvinit, shared libraries, or other things that are essential for the functioning of your system.