SipLine is a free, native Windows SIP softphone built with .NET 9 WPF for maximum performance and reliability. Designed for SMBs, freelancers, and enterprises, it offers enterprise-grade security (TLS/SRTP/DPAPI), HD audio with Opus and G.711 codecs, and real-time call quality monitoring. Unlike browser-based or Electron solutions, SipLine starts in under 0.5 seconds with minimal CPU usage. It works with any SIP provider or IP-PBX — 3CX, Asterisk, FreePBX, OVH, Twilio, RingCentral, and more. Key features: - Free Community plan with no time limit - C# Plugin SDK for custom integrations (CRM, call recording, automation) - Plugin Marketplace for community and premium extensions - Multi-account support (up to 5 SIP accounts) - Professional headset support (Jabra, Poly, Sennheiser, Logitech) - Silent MSI installer with GPO support for enterprise deployment - Real-time call quality metrics (MOS Score, Jitter, RTT) - GDPR compliant — EU-hosted infrastructure (France/Germany) Plans range from free (Community) to custom Enterprise with white-label and unlimited workstations.