Linphone is a popular open‑source SIP client for voice and video calls. Below is a curated list of 20 free (open‑source or free‑tier) VoIP solutions that can serve as alternatives, ranging from desktop/mobile SIP clients to full‑featured PBX/server platforms.
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Web‑based, open‑source video‑conferencing platform with SIP integration and end‑to‑end encryption.
Decentralised, peer‑to‑peer communication app offering voice, video, and messaging without a central server.
Low‑latency, open‑source voice chat primarily for gamers, supporting encrypted SIP bridges.
Lightweight Windows SIP softphone supporting HD audio, video calls, and multiple accounts.
Free version of the 3CX softphone offering SIP calling, video, and instant messaging on Windows, macOS, and Linux.
Cross‑platform SIP client with a modern UI, supporting audio/video calls, presence, and multiple accounts.
Popular multi‑platform SIP client with a free tier, offering HD voice, video, and encryption.
Open‑source VoIP and video conferencing application for Linux and Windows, supporting SIP and H.323.
Android SIP client that integrates with the native dialer, supporting multiple accounts and codecs.
Free Android SIP client that works as a regular phone app, offering call recording and encryption.
Android and iOS softphone from Grandstream, supporting SIP, video, and push‑to‑talk features.
Formerly Ring, an open‑source SIP client for Linux, macOS, and Windows, now merged into Jami.
The original open‑source SIP client that evolved into Jitsi, still usable for basic SIP calls.
Scalable open‑source telephony platform that can act as a softphone gateway, PBX, or media server.
Industry‑standard open‑source PBX that provides SIP calling, voicemail, conferencing, and more.
High‑performance SIP server for routing, load‑balancing, and NAT traversal in large VoIP deployments.
Full‑featured open‑source unified communications suite (PBX, voicemail, conferencing) built on SIP.
Web‑based open‑source GUI for FreeSWITCH, offering multi‑tenant PBX features and SIP trunking.
Open‑source communication platform providing a PBX, VoIP gateway, and API‑driven telephony services.