Outdoor `living lab' experimentation using pervasive computing provides new opportunities: higher realism, external validity and large-scale socio-spatio-temporal observations. However, experimentation `in the wild' is highly complex and costly. Noise, biases, privacy concerns to comply with standards of ethical review boards, remote moderation, control of experimental conditions and equipment perplex the collection of high-quality data for causal inference. This article introduces Smart Agora, a novel open-source software platform for rigorous systematic outdoor experimentation. Without writing a single line of code, highly complex experimental scenarios are visually designed and automatically deployed to smart phones. Novel geolocated survey and sensor data are collected subject of participants verifying desired experimental conditions, for instance. their presence at certain urban spots. This new approach drastically improves the quality and purposefulness of crowd sensing, tailored to conditions that confirm/reject hypotheses. The features that support this innovative functionality and the broad spectrum of its applicability are demonstrated.