Long Term Collaboration
Groups in Office 365 let you choose a set of people that you wish to collaborate with and easily set up a collection of resources for those people to share. You don't have to worry about manually assigning permissions to all those resources because adding members to the group automatically gives them the permissions they need to the tools your group provides. Additionally, groups are the new and improved experience to take the place of distribution lists or shared mailboxes. For more details about Office 365 groups, you can refer to this article: What are Groups?
Microsoft Teams is the chat-centered work space in Office 365. It's the hub for team chats, calls, meetings, and messages. Microsoft Teams is extensible and customizable, and it's secured and standards-compliant to make sure your company's most sensitive collaborations are private. Actually, Microsoft Teams is built upon Office 365 Groups and provides a new way to access shared assets for an Office 365 Group. Microsoft Teams is the best solution for persistent chat among group/team members. For more information, please have a look at the article: What is Teams?
Microsoft boards, you can use it to group and share related documents in Delve. You can, for example, create a board to collect all project documents for your team. It's a little bit different from Office 365 groups and Microsoft Teams and based on Delve. For more information:
Introducing boards in Office Delve - a new way to organize and share work