Delta 4 was a British software developer created by Fergus McNeill, writing and publishing interactive fiction. Delta 4 designed games between 1984 and 1992. Some were self-published, others were released by CRL Group, Piranha Software, Silversoft, or On-Line Entertainment. Delta 4 were also credited with providing the code for Jonathan Nash's tape magazine YS2 which was given away free with Your Sinclair magazine and published by Future Publishing.