1. API Generation and Management: One key difference between PostgREST and Robomongo is that PostgREST focuses on automatically generating a REST API from a PostgreSQL database, allowing for easier API management, while Robomongo is primarily a GUI client for MongoDB, used for data management tasks.

2. Database Support: PostgREST specifically targets PostgreSQL databases, utilizing its features and functionalities, while Robomongo is designed for MongoDB database management, with a focus on NoSQL capabilities.

3. Query Language: PostgREST utilizes SQL for querying data from the PostgreSQL database, making it ideal for those familiar with SQL syntax, whereas Robomongo uses a combination of JavaScript-based queries for MongoDB operations.

4. Authentication and Authorization: PostgREST has built-in support for authentication and authorization mechanisms, providing security features for APIs generated from PostgreSQL databases, whereas Robomongo focuses more on data visualization and manipulation without intricate security features.

5. Platform Compatibility: PostgREST is compatible with various platforms and frameworks, making it versatile for a wide range of development environments, while Robomongo is specifically designed as a cross-platform GUI client for MongoDB, catering to MongoDB users exclusively.

In Summary, when choosing between PostgREST and Robomongo, consider factors such as API generation, database support, query language, authentication, and platform compatibility.