On Joel Spolsky's blog, I often read something about "Wasabi" and if I check Wikipedia, it mentions that it's an in-house programming language.
What is it? Why do they use it? And why isn't it public?
I would start with The Origin of Wasabi:
As the primary developer and maintainer of Wasabi, I've wanted to write a series of articles on Wasabi for awhile, and last week, I decided to talk to Joel about it. Today, I will start off with a short history of the language, and later, I will talk about some of its cooler features and where we want to take it in the future.