In the last years Open source has emerged due to its success in the production of reliable and robust software. Its paradigm about software production, collectively-created programs in a process where users are also developers (to different degrees), has underlined the effectiveness of open and community-based systems compared to proprietary and closed standards, highlighting the cheapness and the flexibility in the adaptation to different situations. This paper aims to investigate the introduction of the open source development methodology in the field of architecture (mainly in the field of living) through the collection and analysis of some recent projects and initiatives, in order to give a first possible definition of open source architecture and trying to identify some of the main directions of action for the design, creation and management of platforms that host trans-scalar community of users focused on transforming the built environment in a sustainable, adaptable and low-cost way. Each case study (including Architecture for Humanity, Wikihouse, Shanghai Air Tree and others) tried to develop, in different forms and methods, some architectural tools based on communities of users that can design and build architectural objects able to respond and adapt to needs of local communities that want to increase spontaneously the quality of public spaces and dwelling. Based primarily on the use of digital information and its ease of transmission, reading and manipulation, and by exploiting also the spread of digital fabrication, the proliferation of electronic devices and accessible design software (eg. Sketchup) and the use of licenses suitable for sharing, the examined cases deepen the theme of open source applied to architecture underlining a complex and dynamic landscape in continuous evolution. The analytical work has led to the categorization and organization of case studies and their subsequent comparison, in an attempt to provide a snapshot view of the phenomenon of open source architecture, in order to assess the possible impacts and consequences for the practice of architecture, the sustainable transformation of the built environment and the ability to deal nimbly new phenomena that affect and change contemporary livin
