GameNetworkingSockets is Valve's production-grade C++ networking library for real-time multiplayer games. In actual operation it provides connection-oriented and message-oriented transport over UDP, with reliable and unreliable message delivery, fragmentation, retransmission, AES-GCM-256 encryption, Curve25519/Ed25519 key exchange, certificate-based authentication, and a full connection state machine. The library also implements peer-to-peer connectivity through ICE/STUN/TURN, WebRTC transport integration, and Steam Datagram Relay (SDR) in Steam builds, plus custom signaling support for non-Steam rendezvous. It is not a standalone application; it is an embeddable SDK whose primary public surface is the Steamworks-compatible C++ interfaces in include/steam (ISteamNetworkingSockets, ISteamNetworkingMessages, ISteamNetworkingUtils) and a flat C ABI wrapper. The main implementation lives in src/steamnetworkingsockets/clientlib, where the SNP reliable protocol, socket thread, direct UDP transport, P2P routing, and connection state machines are implemented, supported by a substantial private utility layer (tier0/tier1 containers, serialization buffers, string utilities) and multiple interchangeable crypto backends.
SIPSorcery is a comprehensive real-time communications library for .NET implementing SIP, WebRTC, RTP/RTCP, STUN/TURN/ICE, DTLS-SRTP, and SCTP protocols from scratch. The core library (src/SIPSorcery) provides SIPTransport for signaling, RTCPeerConnection for WebRTC, RTPSession for media transport, and media endpoint abstractions (IAudioSink, IVideoSource) for decoupling capture and rendering. Satellite projects include SIPSorceryMedia.Abstractions (media interfaces), SIPSorceryMedia.FFmpeg and SIPSorceryMedia.Windows (codec backends), SIPSorcery.VP8 (a C# port of libvpx VP8), SIPSorcery.OpenAI.Realtime (OpenAI Realtime API client), and a CLI tool (SIPSorcery.Cli) with route/bridge commands for wiring media pipelines between SIP, WebRTC, and cloud realtime endpoints.