Complex sentence: It works outside the framework of the U.S. federal government to provide independent guidance and analysis and relies on a "pro bono" workforce of scientists and other experts, operating under a rigorous, formal peer-review system.
Split into simpler sentences: It works outside the framework of the U.S. federal government to provide independent guidance and analysis. It relies on a volunteer (meaning "pro bono") workforce of scientists and other experts and has a rigorous, formal peer review system.