Social computers have been characterised as goal oriented complex systems comprised of humans as well as computational devices. Such systems can be found in natura in a variety of scenarios, as well as designed to tackle specific issues of social and economic relevance. In the present article we introduce the Lightweight Situated Social Calculus (LS 2 C) as a language to design executable specifications of interaction protocols for social computations. Additionally, we describe a platform to process these specifications, giving them a computational realisation. We argue that LS 2 C can be used to design, implement and execute social computations.