Microsoft Teams alternatives

Microsoft Teams
Microsoft Teams is the chat-based workspace in Office 365 that integrates all the people, content, and tools your team needs to be more engaged and effective. Microsoft Teams free open-source (self-hosted) alternatives are: Mattermost, Rocket.Chat, Zulip
Microsoft Teams alternatives are:
Slack, HipChat, Yammer

Here are the latest news about Microsoft Teams:

11.09.17 Microsoft Teams adds guest access

Microsoft announced a number of feature updates to the service Teams. Starting today, you can add anyone with an Azure Active Directory account as a guest to a team. That still means there’s a bit of a barrier to entry here for guest access and Microsoft plans to lower than barrier in the near future by also allowing Teams users to add anybody with a basic Microsoft Account to Teams. Microsoft also announced that 125,000 organizations in 181 markets now use Teams, its Slack competitor for Office 365 subscribers. The conclusion is that Microsoft Teams is now more safe in comparison to alternatives

2017 Microsoft opened Teams to all Office 365 users

2016 Microsoft introduced Teams - the main Slack competitor