Here are the forums for Power BI:

Power Pivot - Discussions relating to importing data, building relationships, and using DAX within the Power Pivot window.

Power View - Power View is an interactive data exploration, visualization, and presentation experience that encourages intuitive ad-hoc reporting.

Power Query - Microsoft Power Query for Excel enhances self-service BI for Excel with an intuitive and consistent experience for discovering, combining, and refining data across a wide variety of sources including relational, structured and semi-structured, OData, Web, Hadoop, Azure Marketplace, and more. Power Query also provides you with the ability to search for public data from sources such as Wikipedia. Power Query was formerly known as Project codename "Data Explorer".

Power Map - Power Map lets you plot geographic and temporal data visually, analyze that data in 3D, and create interactive "tours" to share with others. Power Map was formerly known as Project codename "GeoFlow".

Power BI Q&A - Empower everyone in your organization to quickly get the answers they need by simply asking a question. Power BI Q&A works with data stored in your Power BI site.

Power BI mobile apps - Power BI mobile apps are dedicated native apps for Windows 8, Windows RT and additional platforms to come. Stay connected with your reports and data wherever you are as well as HTML5 support for browser based viewing on any device.
 
Power BI for Office 365 - Microsoft Power BI for Office 365 is a hybrid self-service information management solution that spans cloud and on-premises components and provide search based data discovery for public data and for internal corporate data. It empowers business users to easily and securely find, acquire, augment, manage, and consume information with minimal support from IT. Microsoft Power BI for Office 365 includes BI Sites, Admin Center and Data Steward Portal.