The Hippo OpenSim Viewer is available as compiled binaries and as C++ source code.
Please note that Hippo OpenSim Viewer is based on open source from Linden Lab, however it is not provided or supported by Linden Lab, the makers of Second Life.
Binary packages are available for Windows and Linux.
The latest source code is available from the OpenSimulator Forge Subversion Repositiory.
For building from source code, you will need additional libraries and files that are not checked into the SVN repository. Please refer to the build instructions for more details.