Describe a website you use often

The website I use most often, apart from work things, is a public transport map for Ho Chi Minh City that a group of volunteers built. It's not an official site. What it does is show every bus route on one map, which sounds basic until you try to find that information anywhere else — the official sources list routes separately, so you can see route 8 and route 19 but you can't see where they cross. I use it maybe three or four times a week, usually before going somewhere I haven't been. I've probably had it open a thousand times over four years. Why is it useful? Because it answers the question people actually have. Nobody wants to know the full route of bus 8. They want to know how to get from here to there, and whether it's worth it compared with a bike. That gap between the information that exists and the information people need — that's the whole value of the site. And there's a second thing, which is that it made me use buses at all. Before I found it I assumed the system was unusable, when actually it was just undocumented. Those are very different problems, and I'd been blaming the wrong one for years. It's still run by volunteers, which I think is slightly embarrassing for the city.