Tox
Tox is an encrypted P2P communication protocol implemented through the toxcore libraries. Independent front ends such as qTox, Toxic, TRIfA, and aTox use those libraries for identity, discovery, messaging, calls, and data transfer.
Genuine but uneven client interoperability
Tox has real protocol-level client interoperability: a user of one conforming client can exchange supported traffic with a user of another. The Tox Client Standard exists specifically to define behavior that toxcore does not enforce but clients need for interoperability and security.
This is narrower than saying every Tox feature is portable. The project’s current client matrix shows broad support for one-to-one messages, but uneven support for moderated groups, group history, group audio, inline media, and offline behavior. Some conveniences are client features rather than common protocol guarantees.
Distribution model
Tox is decentralized through direct P2P communication and distributed discovery, not through domain federation. Participants communicate through the Tox network rather than accounts hosted by administrative domains.
Secure and decentralized communication stacks places Tox within the wider secure-communications landscape.