1. PostgREST: PostgREST is an open-source tool that automatically generates a RESTful API from a PostgreSQL database. It allows users to interact with their database using standard HTTP methods such as GET, POST, PUT, and DELETE. The generated API provides a simple and efficient way to access database resources without the need to write custom server-side code.

2. Postgres.js: Postgres.js is a library that provides a Node.js interface for interacting with PostgreSQL databases. It allows users to perform various database operations such as querying, inserting, updating, and deleting data using JavaScript code. Postgres.js provides a low-level API that gives developers full control over the interaction with the database.

3. Database abstraction: PostgREST provides a high-level abstraction on top of the PostgreSQL database, generating a RESTful API that hides implementation details. Postgres.js, on the other hand, provides a low-level API that allows direct interaction with the database, requiring developers to write SQL queries.

4. API generation: PostgREST automatically generates a RESTful API based on the structure of the database schema. It infers the resource endpoints, query parameters, and response formats from the database metadata. Postgres.js does not generate an API but provides a programmatic interface for interacting with the database.

5. Ease of use: PostgREST simplifies the process of building a RESTful API by automatically generating it from the database schema. It reduces the amount of boilerplate code that developers need to write and provides a standardized way to access database resources. Postgres.js, on the other hand, requires developers to write custom code to interact with the database, which can be more complex and time-consuming.

6. Customization: Postgres.js provides a flexible and customizable way to interact with the database. Developers have full control over the SQL queries that are executed and can customize the behavior of the library according to their specific needs. PostgREST, on the other hand, has limited customization options as it generates the API based on the database schema.

In Summary, PostgREST and Postgres.js differ in terms of their approach to database interaction and API generation. PostgREST automatically generates a RESTful API from a PostgreSQL database, providing a high-level abstraction and simplifying the process of building an API. Postgres.js, on the other hand, provides a low-level API that allows direct interaction with the database, giving developers more control but requiring custom code.