1. Transport Protocol: FreeRADIUS primarily operates as a network protocol server and uses the RADIUS (Remote Authentication Dial-In User Service) protocol over UDP or TCP for communication. On the other hand, OAuth2 is an authorization framework that relies on HTTP/HTTPS as the transport protocol to enable secure exchanges between clients and servers.

2. Authentication vs Authorization: FreeRADIUS focuses mainly on authentication, providing a centralized user authentication and accounting system. It is commonly used for various network services, such as Wi-Fi hotspot authentication. Conversely, OAuth2 is predominantly an authorization framework that allows clients to access protected resources on behalf of the resource owner. OAuth2 is often used in web and mobile applications to grant limited access to user data from other services.

3. Scalability and Load Balancing: FreeRADIUS is designed to be highly scalable, enabling it to handle large amounts of network traffic efficiently. It supports features like load balancing and clustering, allowing for the distribution of authentication requests across multiple servers. In contrast, OAuth2 does not inherently provide built-in scalability and load balancing mechanisms. However, these functionalities can be implemented in the underlying infrastructure supporting the OAuth2 framework.

4. User Management and Identity Stores: FreeRADIUS stores user information in its own database or integrates with external identity stores, such as LDAP or SQL databases. It allows for custom user management and flexible authentication methods. OAuth2, on the other hand, relies on existing identity providers (IdPs) for user management and authentication. It utilizes tokens to establish the user's identity and grant access to resources without directly handling user credentials.

5. Authorization Grant Types: OAuth2 offers various grant types to support different use cases. These grant types include authorization code, implicit, client credentials, and resource owner password credentials. Each grant type serves a specific purpose, such as server-to-server communication or user interaction. In contrast, FreeRADIUS does not have explicit grant types but supports multiple authentication methods based on protocols like PAP (Password Authentication Protocol) or EAP (Extensible Authentication Protocol).

6. Scope and Fine-Grained Access Control: OAuth2 provides a mechanism for defining scopes, which specify the level of access a client has to a resource. Scopes allow for fine-grained access control, enabling users to grant specific permissions to clients. FreeRADIUS, however, does not have an inherent concept of scopes. It primarily focuses on user authentication and accounting, allowing or denying access based on broader policies and rules defined in the RADIUS configuration.

In Summary, FreeRADIUS is a network protocol server primarily focused on authentication, scalability, and flexible user management, while OAuth2 is an authorization framework relying on HTTP/HTTPS, driven by scopes, and leveraging existing identity providers for user authentication and authorization.