Complex sentence: The New York Review Books Classics is a publishing house which has as its project reintroducing some of the many remarkable books that have fallen out of print, or simply out of mainstream attention.
Split into simpler sentences: The New York Review Books Classics is a series of titles released under the publishing imprint New York Review Books. This series' project is reintroducing some of the many remarkable books that have fallen out of print, or simply out of mainstream attention.