I had access to a full copy of the original Transport Tycoon Deluxe on PC, and I remember finding myself to be the most creative player in that game, and I recall spending hours and hours and days and nights on it. I left it at one point when I started going to college, and after a long time again, I discovered OpenTTD.
I was very thrilled to find that this game has been ported to an open source project and also has an online system and community of players. I immediately signed up on a popular forum of players and played it competitively, discovered a lot of optimizations and had my fun again all the way. It was absolutely a refresh to see this game. I will end up teaching it to my kids when they come up to the right age again.
A timeless legend of a game, this is.