Whoa, it is still hard to remember that the 90's were not 10 years ago... Now OpenTTD looks old
Anyway, I first played the demo version of TTO back in the 90's, something like 1997 or 1998. I remember figuring the game as a child (even without speaking English), it was really exciting

I really liked the game, and got the full version (still TTO), and I played it quite a lot. I still have some of my old savegames from that time, it's interesting to see what I did with two-way signals only

I had been building point-to-point routes for quite a long time, learning from the old AI...
Then came our new computer, and I was sad to see that TTO didn't work on it. I could do nothing about it at the time.
Several years later, I found out about DOSBox while looking for TTD, but our computer was not strong enough to run the game under DOSBox sufficiently. But it was good to see one of my old favourites again

Shortly afterwards I found OpenTTD (through Wikipedia I believe), the latest stable version was 0.5.3 at the time, the 0.6 branch was in beta. I was amazed to see the quality of the game and the new features (multiplayer, for example). I still consider OpenTTD to be the best open source remake of a classic game.
Interestingly, it was OpenTTD that introduced me to the concept of open source, I got interested in it because of OpenTTD. I was lurking for quite a long time on the forums, the NoAI branch was still separate, I remember seeing NoCAB as a new AI, which was already very strong at the time. I liked the idea of testing AIs against each other, and that is the time when I registered on the forums to post some feedback. I got the idea of making a remake of the old AI, and thus the development of SimpleAI started in 2009.
I'm still here on the forums since then, sometimes actively, sometimes inactively. I'm glad that I could contribute at least a little to this wonderful project.