What distinguishes them from OneBusAway and its real-time when’s-the-next-bus info, is their trip-planning assistance. WhichBus is also built on real-time bus movement, but the interface is based on getting you from Point A to Point B.
It’s beautifully simple (and award-winning). You can write in your locations of choice (or tell it to determine your location for you), and the search function has gotten much, much better at using place names like “Space Needle” instead of requiring specific addresses.
Seattle’s internecine transit system, with its dearth of system and route maps and schedules, makes this kind of service a necessity. But I can’t advise use of WhichBus for newbies yet. For one thing, there’s no app version available — they’re waiting for Apple approval.
For another, you just can’t trust it: To the right, you see it delivering what looks like an impossibly circuitous (if not downright impossible) route from Capitol Hill to the University Village Apple Store. I’ve tested a few routes on it, and it seems overly inclined to direct you to downtown to pick up a transfer to a bus actually heading in the direction you want. Downtown plus a transfer makes almost any trip in Seattle take an hour.
If you’re starting from Seattle Center and trying to get to Capitol Hill, WhichBus quite rightly suggests the #8. But if you’re starting from Capitol Hill, it suggests you take the #10 or #12 downtown, then catch a bus to the Center, which — as slow as the #8 bus is — is usually a longer route. Presumably, all this requires is some algorithmic tweaking, but unless you know Seattle’s bus system well enough to know you’re being had, I’d wait a bit on this.