How to figure out what formula corresponds to a given package in homebrew?
brew desc should search among both formula names and descriptions, and is now included in brew. The site Search Brew also uses this. However, both seem to cover only the default repository, as a quick test on my machine fails to pick up packages in homebrew/python. 

In the specific case of the Parallel Patterns Library, I'm not sure that the entire 'ppl' is actually available on Mac. Microsoft has made a subset of it cross-platform as 'pplx', but otherwise I have no good news.