This paper explores the key features for achieving systems and tools scalability for online learning. We created large scale tools used in popular online courses on teaching and learning programming with Linux that take advantage of client-side web technologies. We advocate for more compatible, interoperable and light tools and systems that are resilient, elastic, traceable, responsive and secure. We also think social features should be considered like friendliness, accessibility, openness and re-usability. Those features could be used to assess the quality and the scalability potential of MOOCs by choosing different metrics to evaluate for each introduced feature. In doing so we hope to diversify the standard indicators of the success of online courses, especially regarding their scalability, and give some examples for STEM courses.