Modular construction

Modular construction is a form of offsite production of building structural units which are then assembled onsite to complete the construction of a building: the modular units form the structure of the building as well as enclosing usable space. Modular construction is particularly popular for hotels, educational facilities such as classrooms and student residences, and healthcare facilities. This is due to the economies of scale available from many similar sized modules and the particular benefit of reduced on-site construction time.
Advantages.
In a 2018 "Practice Note", the NEC states that the benefits obtained from offsite construction mainly relate to the creation of components in a factory setting, protected from the weather and using manufacturing techniques such as assembly lines with dedicated and specialist equipment. Through the use of appropriate technology, modular construction can 
Safety advantages.
Modular construction can help eliminate or reduce many hazards associated with traditional construction, and they can be avoided including: 
The use of modular construction methods is encouraged by proponents of Prevention through Design techniques in construction. It is included as a recommended hazard control for construction projects in the "PtD - Architectural Design and Construction Education Module" published by the National Institute for Occupational Safety and Health.
Modular construction systems.
Open-source and commercial hardware components used in modular construction include: Open beam, Bit beam, Maker beam, Grid beam, Contraptor, OpenStructures components, ... Space frame systems (such as Mero, Unistrut, Delta Structures, ...) also tend to be modular in design. Other materials used in construction which are interlocking and thus reusable/modular in nature include interlocking bricks.