Wordnik – 10 million API Requests a Day on MongoDB and Scala
From the website:
Wordnik is an online dictionary and language resource that has both a website and an API component. Their goal is to show you as much information as possible, as fast as we can find it, for every word in English, and to give you a place where you can make your own opinions about words known. As cool as that is, what is really cool is the information they share in their blog about their experiences building a web service. They’ve written an excellent series of articles and presentations you may find useful: (see the post)
Of course, what I find fascinating is the “…make your own opinions about words known” aspect of the system.
Even so, from a scaling standpoint, this sounds like an impressive bit of work.
Definitely worth a look.