"Many large corporations are famous for keeping this type of tool under lock and key, but we think we stand to gain much more by collaborating with other smart companies and developers."

Is Facebook in some unique position to be releasing big parts of their infrastructure like that? Why don't companies do it more often?

Although this isn't the same thing as Ruby on Rails, and not to be overly cynical, but could this be a new form of community-building-based PR... in the sense that the goodwill/PR value of the FOSS community is worth more to Facebook than the value of keeping Thrift proprietary?