Age of steam was first and then he designed Railroad Tycoon which was a streamlined AoS. More family friendly. Not sure if it was a tie-in to the Sid Meier game of the same name, but I think they were related.
Then Glenn Drover jumped on it and polished some of the rough edges and it became Railways of the World.
Steam, I believe was the last iteration. Came out after both of the others. Tried to polish AoS while maintaining the heavy-euro aura.