Zulip is a real-time chat service (similar to Slack, Twist, or Gitter) that incorporates a threading model similar to email. It claims to allow users to "catch up on important conversations while ignoring irrelevant ones." More than 90 integrations with popular services are available, including GitHub, Jira, Strip, Zendesk, and more. As with other services in this space, it supports drag-and-drop file uploads, images inline in chats, and provides previews of external links. Unlike many similar offerings, Zulip is an open free software and can be self-hosted. Source code is available on GitHub under the Apache license. To self-host, the Zulip developers recommend a dedicated machine or cloud server with at least 2GB ram and 10GB of disk space. Detailed instructions for installation on Ubuntu servers are provided. For users that do not wish to self-host, Zulip's free hosted offering includes 10k messages of search history and 5GB of storage for uploaded files. Users can connect to a Zulip server either through their browser, using one of the native desktop apps (available for Windows, macOS, and Linux), using a smartphone app (iOS or Android), or with a number of multi-protocol chat programs.