Which of the following is similar to RDP but is fully cross-platform and open-source?

The correct choice is Virtual Network Computing (VNC) because it is a cross-platform, open-source solution that allows remote control of a computer over a network. Unlike RDP, which is primarily designed for Microsoft Windows environments, VNC works across different operating systems, including Windows, macOS, and Linux. This versatility makes it suitable for a wider range of applications and environments where users may need to access a remote desktop regardless of the underlying system architecture.

VNC operates on a client-server model, where the server component runs on the machine that is being accessed remotely, and the client runs on the user's machine. This approach enables users to view and interact with the graphical desktop environment of the server machine from virtually any device capable of running the VNC client software.

The other options do not provide the same combination of cross-platform compatibility and open-source nature as VNC. Unified Communications is a broader term referring to integrated communication solutions, while RDP is proprietary to Microsoft and not fully cross-platform. Traffic Mirroring pertains to network traffic analysis and does not relate to remote desktop access at all.