The 'alien' command does that: http://kitenet.net/~joey/code/alien/
It is in Trisquel's repositories.
However, read and reread the warning on the site of the command:
Despite the large version number, alien is still (and will probably always
be) rather experimental software. It has been used by many people for many
years, but there are still many bugs and limitations.
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 can't uninstall the package without
breaking your system, don't try to replace it with an alien version.
