In a similar spirit to Freedoom, for Quake fans perhaps you'll want to take a look at LibreQuake, which aims to do a similar thing to allow you to play Quake content with completely open source software.
This is not an engine, this is the freedoom equivalent for quake. You will need a quake engine like QuakeSpasmSpiked and then follow the how to play instructions.
This is not an engine, this is the freedoom equivalent for quake. You will need a quake engine like QuakeSpasmSpiked and then follow the how to play instructions.