Sixty-four custom entities were made. Search the file for “GRAVITY BONE CUSTOM ENTITIES” to find these custom entities. There’s some sparse documentation but you might need to peek into TFOL’s source code to find details on how things work.
I used GTKRadiant 1.3.13 to make maps for GB & TFOL. For GTKRadiant to recognize the entity definition file, place the file into the Thirty Flights of Loving folder: