GV Research Sprint
Google Venture uses a four-day sprint to validate ideas with real users. It is build to rapidly get feedback and integrate in your product. This can be used for all kind of products that would benefit from user research. This page links to a series of articles that explain the concept behind it.
The original content can be found here GV’s Guide to UX Research for Startups or can be read in the book Sprint (How to Solve Big Problems and Test New Ideas in Just Five Days) which can be found in our book shelf.