Small modular reactors (SMRs) are currently touted as the next evolution of nuclear energy. They are a type of nuclear reactor designed to be smaller in size than a traditional reactor. Nevertheless, they are based on the same fission technology that splits atoms to create heat, which can then be used to generate electricity. SMRs can offer clean, reliable power and heat at manageable costs for both on- and off-grid communities. Currently, there are more than 100 proposed SMR reactor designs worldwide participating in the race to commercialization. This article presents a comprehensive review of the different SMR technologies that are currently being developed. The technical characteristics of the SMRs have been evaluated to provide insights into their complementary role in a renewable energy system and highlight how they can accelerate the journey toward a deeply decarbonized world.