Cross-platform building
From the 2.0 version, OSG starts to make use of a powerful build system—CMake. This can be used to configure software compilation processes with a compiler-independent scripting language. With simple configuration files, CMake can generate native makefiles and workspaces that can be applied to various compilation environments and platforms. That is why an increasing number of projects, such as KDE, VTK, Boost, MySql, and OpenSceneGraph, choose CMake for cross-platform building.
You may download the CMake binaries or source code at: http://www.cmake.org/cmake/resources/software.html.
After that, you may start to download the latest OSG source package or any previous version you are interested in. Be aware that there are usually two different kinds of OSG versions: stable releases and developer releases. For end-users, the former is preferred because of their stability. And for software developers and community contributors, the latter will be at the cutting edge and will always contain exciting new features, although you may occasionally see build and runtime errors on particular platforms.
OSG uses odd minor version numbers to denote developer releases and even minor version numbers for stable ones. For example, OpenSceneGraph 2.8 was the previous stable release branch, based on the work that was done in the 2.7.x versions. Then the 2.9.x versions were intermediate versions leading to the latest stable release family, named OpenSceneGraph 3.0. The patch version after the minor version number is used to denote very minor changes and bug fixes.
Stable source code can be downloaded from: http://www.openscenegraph.org/projects/osg/wiki/Downloads.
And for early adopters, remember to keep track of the latest developments at: http://www.openscenegraph.org/projects/osg/wiki/Downloads/DeveloperReleases.
The link to the SVN repository, which is even more bleeding-edge but requires a subversion client (for example, TortoiseSVN) to check out the source code: http://www.openscenegraph.org/projects/osg/wiki/Downloads/SVN.