Second language teaching and learning has experienced a change towards the use of mobile technologies inside and outside the classroom. The goal of this article is twofold: to compare and evaluate three different commercial English language learning apps (Duolingo, Babbel, and Busuu) that cover the four skills (speaking, writing, listening, and reading), and to analyze the learning theory supporting their design. These applications include in their homepage the option of interactive learning with friends. However, as this article shows, each app offers a different level of interaction and collaboration. The theoretical framework for this analysis is grounded on Vygotsky's Socio-cultural theory.