Recently modular monolith architecture has attracted the attention of practitioners, as Google proposed "Service Weaver" framework to enable developers to write applications as modular monolithic and deploy them as a set of microservices. Google considered it as a framework that has the best of both worlds and it seems to be a trend in software architecture. This paper aims to understand the definition of the modular monolith in industry and investigate frameworks and cases building modular monolith architecture. We conducted a systematic grey literature review, and the results show that modular monolith combines the advantages of monoliths with microservices. We found three frameworks and four cases of building modular monolith architecture. In general, the modular monolith is an alternative way to microservices, and it also could be a previous step before systems migrate to microservices.