Jami (formerly GNU Ring, SFLphone) is a SIP-compatible distributed peer-to-peer softphone and SIP-based instant messenger for Linux, Microsoft Windows, OS X, iOS, and Android. Developed and maintained by the Canadian company Savoir-faire Linux, and with the help of a global community of users and contributors, Jami positions itself as a potential free Skype replacement. Jami is free and open-source software released under the GNU General Public License. In November 2016, it became part of the GNU Project. Two account types are currently available, and many of each type can be configured concurrently. Both types offer similar features including messaging, video and audio. The account types are SIP and Ring. A SIP account enables the Jami softphone to connect to a standard SIP server and a Ring account can register (or use an account set up) on the decentralised Jami network which requires no central server. However, Jami still has to use bootstrap server to connect making it not a truly internet free communication platform as its claim. By adopting distributed hash table technology (as used, for instance, within the BitTorrent network), Jami creates its own network over which it can distribute directory functions, authentication and encryption across all systems connected to it. Packages are available for all major Linux distributions including Debian, Fedora, and Ubuntu. Separate GNOME and KDE versions are available. Documentation is available on Ring’s Tuleap wiki. On 18 December 2018, Ring was renamed Jami.
Jami seems to be 100% trade-free: unlimited, ad-free, private, compatible, fast, autonomous and anonymous. I wouldn’t consider creating an account which is necessary to use it as a trade, since you can just put any username and a password or not and you don’t need to provide any personal information about you. Here’s the website where you can download jami: https://jami.net/