MongoDB Stitch is MongoDB's serverless platform offering. It is based on four distinct areas of functionality:

• The first area is QueryAnywhere. QueryAnywhere allows client-side applications to access MongoDB using its query language. We can define data access rules on the Stitch server on a per collection basis to allow us to filter results based on user data (userId).
• The second area is Stitch functions. These are simple JavaScript functions that can execute without a server inside the Stitch platform. By using Stitch functions, we can implement application logic, expose APIs, and build integrations with third-party services. This service is mostly similar to Amazon's AWS Lambda.
• The third area is Stitch triggers. Similar to MongoDB server's change streams and triggers as they are used in relational databases, Stitch triggers execute user-defined functions in real time by responding to changes in database state.
• Finally, there is Stitch Mobile Sync, which bridges the Stitch serverless offering with Mobile MongoDB. By using it, we can develop a Mobile service with a local MongoDB database residing in the smartphone, which is perfectly synced with our MongoDB Atlas-powered database in the cloud.

This way, we can query data locally in the app with no lag, or even while being offline, and rely on Stitch Mobile Sync to keep our data store up to date.