Converse.js is a JavaScript-based client for Jabber (XMPP) chat servers. It can be run in any modern browser. End-users can use the public conversjs.org site to connect to their chat service without the need to install dedicated chat software (e.g., from a machine in a computer lab). Converse.js site can connect to any Jabber server that can be reached from the internet, including both public jabber providers and private servers. On servers that support account registration, Converse.js can even be used to create new accounts. Site owners can integrate Converse.js into their own sites in order to provide chat services for their users. Integration plugins are available for Ruby on Rails, Plone, Django, Wordpress, Roundcube, and others. Converse.js is free software, licensed under the Mozilla Public License, with source code available on Github.