Transport Tycoon !! Not deluxe or any fancy thing, the plain old Transport Tycoon, 1st release edition. I actual just looked it up how old it is and it say release 94' so, 17 year old
And yes, it is still awesome! Not long time ago I took it up again, just to first realise that it won't run on vista. Not a big surprise, but it was a surprise that I found it was made open source and I could get a improved version of it with tons of new stuff... ohh yes... there went a god handful of hours that way again.