The Realm C++ Preview is a new software development kit (SDK) announced by MongoDB, which provides developers with a comprehensive solution for building distributed applications that securely use data at the edge. The SDK offers capabilities such as network handling and conflict resolution, real-time use cases, and an object-oriented database without requiring a separate mapping layer or ORM. It also introduces an improved syntax for defining object models, automatic schema discovery, and support for Windows operating systems. This release is part of MongoDB's mission to provide developers with seamless technologies that make the development process easier.