Microsoft Teams vs Slack

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
Slack brings all your communication together in one place. It's real-time messaging, archiving and search for modern teams. Create open channels for the projects, groups and topics that the whole team shares. Slack searches whole conversations, not just individual messages, so you can find what you’re looking for no matter who said what or when they said it. Slack free open-source (self-hosted) alternatives are: Mattermost, Rocket.Chat, Zulip
Slack has better video than Microsoft Teams

2018 - Microsoft Teams will integrate with Cortana to defeate Slack

Microsoft Teams, the company’s team collaboration software and challenger to Slack, announced a suite of new features that will roll out to the software throughout 2018. This includes features that will allow users to record, transcribe and save meetings to the cloud, integrations with voice assistant Cortana, inline message translation and several others. The added integration with Cortana’s voice assistance could give Microsoft an edge in its battle with Slack, given the increasing importance of voice-based computing in the workplace and within business productivity applications.

2018 - Microsoft Teams gets new app integrations and app store to keep up with Slack

Microsoft Teams, rolled out its biggest update since the software’s launch last year. The focus of the new set of features is allowing users to better work with apps – something Microsoft Teams accomplishes via Slack-like integrations, search and discovery features, commands, and more. For example, Microsoft Teams now offers a way to search for apps from the new app store where you can browse by category or search by name, category or integration type – like Project Management or BI. Slack, of course, also has its own app directory, which has allowed it to highlight all the work tools that currently work with its team collaboration resource – a move that helped it gain traction in the workplace. The conclusion is that Microsoft Teams is now more integrative than Slack

2016 - Google and Slack team up against Microsoft and Facebook

Recently Microsoft and Facebook launched their clones of popular collaboration service Slack (Teams and Workplace respectively). Of course for Slack it's a tough competition, so they found a partner in face of Google. The companies signed the strategic partner agreement and soon will tightly integrate their product. In particular, Slack will become available as an app in G Suite (formerly Google Apps), so admins will be able to turn it on/off for their users. And inside Slack you'll be able to preview documents via Google Docs editors, and sync access rights for files attached from Google Drive. Besides, Slack will get integration with the new service Google Team Drives (it's the recently launched team-focused version of Google Drive).

2016 - Microsoft introduced Teams - the main Slack competitor

In the beginning of the year Microsoft wanted to acquire super-popular group chat software Slack, but then decided to build the same own service from the scratch. And here it is - Microsoft Teams, and it looks very similar to Slack. You can create rooms for projects or departments, communicate from desktop or mobile devices and share files and other content. Like Slack, it features bots for notification and auto-replies. The main advantages of Teams (according to Microsoft) are its security and tight integration with other Microsoft applications, like Skype, Word, SharePoint, Planner and OneNote. Teams will be available for free in business subscription plans of Office 365. So Microsoft hopes that it will become the last straw for those companies that still don't use Office 365. Teams is now in preview mode and will be generally available in early 2017.