Bitcoin donations also accepted at GNU/Linux systems
Executable versions of Octave for GNU/Linux systems are provided by the individual distributions. Distributions known to package Octave include: Debian, Fedora, Gentoo, and SuSE. These packages are created by volunteers. The delay between an Octave source release and the availability of a package for a particular GNU/Linux distribution varies. The Octave project has no control over that process.
BSD systems
Executable versions of Octave for BSD systems are provided by the individual distributions. Both FreeBSD and OpenBSD have Octave packages. These packages are created by volunteers. The delay between an Octave source release and the availability of a package for a particular GNU/Linux distribution varies. The Octave project has no control over that process.
OS X
The Wiki has some instructions for installing Octave on OS X systems.
Windows
Cygwin
There is an Octave package for Cygwin.
MinGW
The Wiki has some instructions for installing Octave on Windows systems.
Sources
The latest released version of Octave is always available from ftp://ftp.gnu.org/gnu/octave.
If you are interested in working with the latest version of the Octave sources, check out the resources for developers.