This is probably old news to this group but I came across it today and thought it might be of passing interest
"Welcome to the world of railway signalling! SimSig brings the signalbox to your home PC, and with it the enjoyment and frustrations of a running today's railways.
SimSig is free and, as such, is not regularly maintained. However, updates do happen from time to time and we may bring out a new simulation every now and again, so keep visiting the site!"