Microsoft Teams - a part of the Office 365 ecosystem
Microsoft Teams is threaded persistant chats or conversations where the Activity view can be seen as the "inbox" in Teams. A Team "channel" can be seen as the digital equivalent of an ad-hoc meeting in a normal Office environment. Moving images, emojis, stickers, or GIFs, can easily be pasted into team conversations. Microsoft Teams builds on Office 365 groups, and has built-in access to PowerBI, Graph, SharePoint, OneNote, and Skype for Business. A "team" is simply a group of people organized around a common goal, and a sharepoint site is automatically created for each new Team that is created in Microsoft Teams.
Bots are included in Microsoft Teams from start. T-bot can answer questions about the MicorosftTeams product, like: How do I create a channel? Who-bot can answer questions about people. Polly is a poll / voting bot can be used in conversations. Currently some 85 bots are available.
In general, a web browser is all you need to access Microsoft Teams and mobile clients are available as well.
Preview now, General Availability next year.