PrBoom is a source port, derived from the MBF branch of Boom, developed by Florian Schulze, Colin Phipps and Andrey Budko. The latter also maintain a version with many additional features, called PrBoom+. An OpenGL renderer is available as a different executable, called GLBoom (or GLBoom+). All of them feature full Doom, Boom and MBF demo compatibility.
Development for PrBoom has mostly ceased, however PrBoom+ is still actively developed and enhanced with new features, as long as they do not alter gameplay: PrBoom+/GLBoom+ supports extended nodes (but not compressed nodes), GLDEFS skyboxes, the MUSINFO lump, etc.