1. Data Compression Algorithm: One key difference between Facebook and zlib is the primary function they serve. Facebook is a social media platform used for connecting with people and sharing content, whereas zlib is a data compression library designed for reducing the size of files or data streams.

2. Target Audience: Another difference lies in their target audience. Facebook caters to a wide range of users looking to engage socially, whereas zlib is more tailored towards developers and programmers who need efficient data compression solutions for their applications.

3. License and Usage: Facebook is a free social media platform for users, but zlib is open-source software released under the zlib license, allowing developers to use it freely in their projects, commercial or non-commercial, without restrictions.

4. User Interface vs. Library: Facebook provides a user-friendly interface for accessing its features, whereas zlib functions as a library that developers can integrate into their software to enable data compression capabilities.

5. Networking vs. Data Compression: Facebook focuses on social networking features like connecting with friends, sharing updates, and joining groups, while zlib is specifically designed for efficient data compression and decompression tasks in software applications.

6. Public vs. Developer-Focused: Facebook is a publicly accessible platform for all users, while zlib is predominantly utilized by developers and programmers for implementing data compression algorithms in their projects.

In Summary, Facebook is a social media platform for connecting people, while zlib is a data compression library primarily used by developers.