The technologies in question include things like memcached which was created in 2003 by LiveJournal and has been used longer than Facebook has been alive.[…]
Other examples include Open Compute, an open hardware project started by Facebook that focuses on low-cost, energy efficient server and data center hardware; Tornado a Python-based web server used for building real-time Web services; and HPHP, a source code transformer that turns PHP into C++.
I have no other details about this patent letter Yahoo sent Facebook, but I seriously doubt it targets these technologies separately. Most probably it refers to some sort of combinations of these and one that Facebook has mentioned as part of their IP.
Original title and link: Yahoo Patent Letter to Facebook Referring to Memcached and Other Open Source Technologies ( ©myNoSQL)