Alien allows you to convert LSB, Red Hat, Stampede and Slackware Packages into Debian packages, which can be installed with dpkg.
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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. Many of these packages are set up differently by Debian and Red Hat, and packages from the different distributions cannot be used interchangably. In general, if you cant uninstall the package without breaking your system, dont try to replace it with an alien version.