Which of the following is a popular open-source solution that includes TSC functionality?

Asterisk is a widely recognized open-source software implementation of a telephone private branch exchange (PBX) system that incorporates Tactical Session Controller (TSC) functionalities. It is primarily used for managing calls and session handling in VoIP (Voice over Internet Protocol) communications, making it an excellent platform for developers and businesses looking to customize their telecommunication solutions.

The flexibility and robust feature set of Asterisk allow it to support various protocols and integrations, which are essential components of TSC operations. Its open-source nature means that developers can modify and adapt it to suit specific needs, which is a fundamental aspect of many TSC applications. This capability to tailor the software enhances its value in tactical communication environments where adaptability and control of sessions are necessary.

The other options listed (Zoom, Skype, GoToMeeting) are primarily commercial products designed for video conferencing and online meetings, lacking the open-source characteristics and the extensive telephony management capabilities integral to TSC functionality found in Asterisk.