Off course Slack is market leader in terms team collaboration and Chat but here are the list of 4 open source alternatives to Slack for team collaboration and Chat.
Slack offers a lot of IRC-like features: persistent chat rooms (channels) organized by topic, as well as private groups and direct messaging (again, historically based on IRC). All content inside Slack is searchable, including files, conversations, and people. Slack integrates with a large number of third-party services and supports community-built integrations. Major integrations include services such as Google Drive, Trello, Dropbox, Box, Heroku, Crashlytics, GitHub, Runscope and Zendesk. In December 2015, Slack announced their app directory, consisting of over 150 integrations that users can install. Read more click here
Reference:- This article was originally posted on scmgalaxy.com