Mastodon

Mastodon is a decentralized social networking service that provides a free, open‑source microblogging platform built on the ActivityPub protocol. Users can publish short posts, follow accounts, and engage in conversations across independently operated servers known as instances while retaining ownership of their data. The software can be downloaded and installed by anyone who wishes to run their own instance, allowing communities to define their own rules, moderation policies, and feature sets. Unlike ad‑driven platforms, Mastodon does not display advertisements or rely on algorithmic feeds; instead it presents a chronological timeline and gives instance administrators full control over content policies. The service includes built‑in tools such as content warnings, custom emojis, polls, and the ability to lock or mute accounts, which support nuanced expression and community safety. Mastodon appeals to individuals, groups, and organizations that prioritize privacy, data sovereignty, and a community‑governed alternative to centralized social networks.

The organization's flagship server, mastodon.social, is operated by Mastodon gGmbH, a German non‑profit entity that stewards the Mastodon codebase and maintains the primary public instance for users. On 20 April 2026 mastodon.social experienced a distributed denial‑of‑service attack that began around 13:00, caused a major outage, and was mitigated by 16:00 the same day, with the attack ceasing by 11:00 on 21 April 2026; the threat actor 313 Team claimed responsibility but the claim remains unverified. Mastodon’s distinguishing attributes include its federated architecture, open‑source licensing, absence of centralized monetization, and the capacity for each instance to enforce its own moderation standards. These characteristics position Mastodon within the broader social‑media sector as a privacy‑focused, community‑driven alternative to ad‑supported platforms. Ownership of the project rests with the non‑profit Mastodon gGmbH, which oversees development, maintains the flagship server, and coordinates with the wider network of independent instances. The incident in April 2026 highlighted both the visibility of the flagship instance and the resilience measures that the organization has in place to defend against large‑scale disruptions.