You can download the last release of the library here. The current stable version is v0.9.0.
Take a look at the release notes to see what is new in the last version.
The source package of the current release of the library is available in two versions. Either in .zip or .tar.gz format. This package contains the source code, the CMake files necessary to build the library, the documentation and the testbed application with demo scenes.
You can also clone the library on Github. Note that the “master” branch always contains the last released version. This is the most stable version.