Abstract: This essay discusses the notions of “extension” and “prosthesis” as two different logics and modes of being with technology. I trace the two terms to the work of Marshall McLuhan, influenced by the work of Norbert Wiener and Buckminster Fuller. I argue that the logic of softwarisation is similar to the logic of extension, while the logic of appification is similar to that of prosthesis. I argue that these logics also map onto the logics of metonymy and metaphor. I explain why such a distinction is useful for reading mobile apps and the computing practices they enable. I conclude by raising questions about users’ complicity within the bio-technological cybernetic assemblage: What does the user of these technologies want? Is she able to confront her desire through their use? Why is the demanding swarm of parasitic ‘media species’, such as apps, so determined to get under the user’s skin?