Mozilla Thunderbird is a free, open source, cross-platform email, news, and chat client developed by the Mozilla Foundation. The project strategy was modeled after that of the Mozilla Firefox web browser. Thunderbird is an email, newsgroup, news feed, and chat (XMPP, IRC, Twitter) client. The vanilla version was not originally a personal information manager, although the Mozilla Lightning extension, which is now installed by default, adds PIM functionality. Additional features, if needed, are often available via other extensions.