Blasphemer is a free content replacement for the Heretic IWAD, similar to Freedoom for Doom and Doom II. In addition to its own campaign, with currently three episodes and a deathmatch set called BlasphDM available, it allows the playing of custom PWAD mapsets without purchasing the original game.
The project to do similar for Hexen was called Zauberer, later restarted as the Blasphemer tied Lastermaul, while another attempt for Hexen II was called Haktoria. The source code for Heretic II meanwhile was never released, the game has not been released digitally, and has not as yet been reverse engineered onto the released Quake II engine source code.