Proprietary: Free (as in freedom, not price) software puts the user in control by allowing you to use the software for any purpose, modify it, and redistribute it. Non-free or proprietary software, on the other hand, witholds one or more of these freedoms, giving the developer of the software unjust power over the users.
End-to-End Encryption (E2EE): Allows two or more end-points to communicate confidentially, such that no one in the middle (including the service operator) has access to the contents of the communication. This represents a baseline requirement for recommendation in this guide.
Facebook claims that WhatsApp utilizes E2EE for messages exchanged between users. Because WhatsApp is proprietary and the source code cannot be examined, however, it is difficult to back up claims about features such as E2EE. Such privacy measures should be assumed ineffective until proven otherwise (by providing the program’s source code).
Even with E2EE in place, it is possible for Facebook to analyze metadata and even message content from the app itself for the purposes of building a profile on the user for targeted advertising.
Centralized: Centralized services are operated and controlled by a single entity, putting the operator in the position of gatekeeper with total power over your use of the service. Centralized systems also suffer from a single point of failure and are vulnerable to censorship both by the operator and by governments with jurisdiction over the operation of the service.
Limited Interoperability: Interoperability increases freedom and usefulness by allowing different systems to work together. When a service is hostile to other services interoperating, particularly a communication service, this places users in a walled garden, which limits choice and can make it difficult to switch to or from an alternative.