There are several references to other games in RTP, and 1 remaining crossover scene (where a package is exchanged between our MC and the MC from "Our Fate"). There's a poster for "The Way" visible on a wall in Series 1, a brochure for "Personal Trainer" in Series 2, oh and there's also a fun cameo appearance from another character from Our Fate in Series 2.
As others mentioned, the Acting Lessons crossover, which was extensive at the time was removed when that other developer changed his mind and requested it. We always get permission in advance, but there's little you can do about people changing their minds.
