This is intended for rendering PostScript or PDF documents using Ghostscript. Ghostscript has the option -dNumRenderingThreads but it does not speedup pretty much, because it renders each page using multiple threads. This program runs Ghostscript multiple times on distinct page subsets, such that Ghostscript can render pages in parallel. gs-parallel has its own options, interprets them and converts and passes them to gs, but it also allows to pass custom options to gs after --. Run it like so: