Scilab is available as a binary package. However, we are working closely with GNU/Linux & *BSD distributions to create better packages. If you are a packager and you have some questions, need to commit patches upstream or remarks, please contact the Scilab Dev Mailing List or Sylvestre Ledru <firstname.lastname@example.org>.
Debian is an non profit organisation. There are plenty of developers who manages the distribution (packages, bug fixes, architecture...).
Debian overview of the packages : http://packages.qa.debian.org/s/scilab.html
Debian bug report for Scilab : http://bugs.debian.org/cgi-bin/pkgreport.cgi?src=scilab
SVN Debian packages sources http://svn.debian.org/viewsvn/debian-science/packages/scilab/trunk/
Compilation report on various arch https://buildd.debian.org/~luk/status/package.php?p=scilab
Usually, Ubuntu packages are those from Debian plus sometime a few modifications. Ubuntu Scilab packages are created from Debian's and sync regularly.
Home of the package https://launchpad.net/distros/ubuntu/+source/scilab/
Bug tracker ubuntu https://launchpad.net/distros/ubuntu/+source/scilab/+bugs
There is a package done by the Italian Slackware Community http://repository.slacky.eu/slackware-12.2/scientific/scilab/5.1/
There is a package done by Simon Lipp: http://aur.archlinux.org/packages.php?ID=19897
Scilab exists in Mandriva. Mandriva has joined the Scilab Consortium.
Scilab Toolbox ANN : http://cvs.mandriva.com/cgi-bin/viewvc.cgi/contrib-SPECS/scilab-toolbox-ANN/
Mandriva bug tracker : http://qa.mandriva.com/
Gentoo is also a non profit organization. The main principal of the distribution is "compile everything with optimization for your CPU". The dependency tool (emerge) is very efficient.
Markus Dittrich <email@example.com> is the gentoo maintainer for a few scientific packages including Scilab. He is doing a good working on the gentoo packaging of scilab (few patches). Scilab 4.1 & 4.0 are available.
Gentoo overview of the packages : http://www.gentoo-portage.com/sci-mathematics/scilab
CVS gentoo packages sources http://sources.gentoo.org/viewcvs.py/gentoo-x86/sci-mathematics/scilab/
The work on the Scilab 5.X package http://bugs.gentoo.org/237572
Fedora is the community/testing version of the well-known RedHat distribution.
Package database information https://admin.fedoraproject.org/pkgdb/acls/name/scilab
Compilation report http://koji.fedoraproject.org/koji/packageinfo?packageID=12847
Fedora bug report for Scilab : https://bugzilla.redhat.com/buglist.cgi?component=scilab&product=Fedora
FreeBSD is a free (as speech and beer) Unix. A package is call a "port". They packaged the latest version of Scilab (4.1).
FreeBSD patches for Scilab : http://www.freebsd.org/cgi/cvsweb.cgi/ports/math/scilab/ http://www.freshports.org/math/scilab/
Suse / OpenSuse
Scilab is available for both Suse & OpenSuse