OpenTTD is a strong argument in favor of the belief that the open source movement is a product of and directed by Satan. Its earthly form is that of a totally free, cross-platform clone/recreation/whatever of Transport Tycoon Deluxe, only with careful improvements to gameplay, your basic twiddling of knobs and smoothing of corners, such that all the little hinky shit that could get on your nerves and make you stop playing in irritation are gently smoothed away.
In practice, when you start it up... you remember those ghost traps, in Ghostbusters? Yeah, it's like that. Some asshole in a brown jumpsuit hits the switch and you get inescapably sucked in, and before you know it you're stuck in some goddamn containment unit and it takes a man with no dick to get you back out.
Okay, that analogy got away from me a little. But it's very absorbing.
Details and Fiddly Shit
What the hell is Transport Tycoon? It's a sim game of sorts; you play the owner of a fledgling shipping business and you have to make it a marvelous shipping business by the year 2050, by building planes, trains and automobiles and designating routes for them and such. Transport Tycoon Deluxe was the sequel to the original Transport Tycoon and we may or may not have nodes on both of those.
What's the gameplay like? It's pretty micromanagey is what it's like. You have to give your little vehicles explicit instructions on what to do and under what conditions and suchlike. I like to give them fairly simple instructions, but I'm pretty sure that vehicle behavior is a rabbit hole you can dive exactly as far into as you like.
If you like the modern classic Dwarf Fortress you'll probably find OpenTTD both inviting and a breeze, if somewhat pacifistic. If SimCity or Animal Crossing bores the shit out of you, OpenTTD is probably not for you.
Assuming you do like the basic game type, and especially if you have some mild obsessive traits, I warn you again that the game is extremely engrossing. It's somewhere between fun and hypnotic to watch the little cities grow as you ship goods and people to them, your little trains and buses become old and need replacing, and technology advances apace, providing you with new vehicles like monorails and hovercraft. There are some specific moments which are extreme slogs — I am thinking here specifically of replacing 100+ superannuated buses by hand, all at once — but I'm pretty sure there must be a script for fixing that, which I just neglected to download. Besides such incidents, the game rarely becomes tedious — and if it does, there is a handily provided fast-forward button.
I'm pretty sure with this game, you either go »blech« or get stuck hard.
Will it run on my...? Yes. No question. Inarguably. The system requirements are a Pentium II and 64 MB of RAM. Do you have 64 MB of RAM? Probably. You'd have to work pretty hard not to. As for your operating system, it supports fucking BeOS. There is no possible way this can not work on your machine. You'd have to design it expressly for that purpose. Buy vintage computer parts and run that new Chinese operating system on it — although I hear that's mostly cribbed Android, so maybe it will work anyway.
How do I set it up? OpenTTD is very flexible and helpful in some ways. It's designed to be extensively compatible with the original Transport Tycoon Deluxe, so if you have a copy of that game, you can use all the original graphics and sounds and music. If you don't, you can get all-new, also-free honking noises and pictures of apartment buildings along with the game. This is actually one of the few problem areas: being open-source, nobody thinks it's important for the game to have a convenient package solution, so you have to either download four different things, or download one and pull three off your copy of Transport Tycoon Deluxe, and concatenate them for a full game. Otherwise it won't run — I think. Maybe it will just help you download that shit. I wouldn't be surprised, on closer reflection.
For everything else, however (such as, importantly, AIs for computer opponents) there is an in-game download system which is reasonably user-friendly. The main problem with it is a lack of any real overview. Which AIs are good? What do they really do? Are any officially sanctioned by the developers, or even made by them? If so, why are those not included with the game proper? Fuck you, that's why.
[Update, almost immediately: I am informed that for Windows and Linux there are installers which will auto-download everything you need to play, and you can also apt-get the game if you are on a system which supports that. This ignorance on my part is brought to you by the Apple Macintosh, red-headed stepchild of computer gaming.]
Okay, I've decided I want to ruin my life. Where can I get it? You can get it at OpenTTD.org.