Microsoft Planner is a task management app that lets teams organise work on visual task boards, with buckets, due dates, progress and charts. It is part of Microsoft 365 and is also available within Microsoft Teams and SharePoint. Planner runs on Microsoft Graph and the Microsoft 365 group service, and file attachments are stored in SharePoint. It is a proprietary Microsoft service, not open source.
Microsoft is headquartered in Redmond, Washington, in the United States. Under the EU Data Boundary, Microsoft 365 data for tenants with a sign-up location in the EU or EFTA is stored and processed in European datacentres, with limited transfers, and Multi-Geo tenants are excluded. Outside that scope, and for some support and logging processes, the United States can still be involved. A European organisation should check its tenant location, its status in the EU Data Boundary and Microsoft's Products and Services Data Protection Addendum before use.