Power BI Designer Preview is a standalone tool for building reports for Power BI. I'm using it myself whenever I can to build reports - it has all the new visualizations that the Power BI Preview service (www.powerbi.com) has, but in a streamlined client tool. It includes all the Power Query capabilities that are available as an add-in to Excel 2013. If that's not enough, it has the modeling capabilities of Power Pivot, but not all of these are enabled yet in the UI. I has both a 32bit and 64bit version - so you can get the best experience for your computer. Key thing is it's free to download and use. While it's still an early preview, it's also amazing how much you can do in Power BI Designer.
Here's where you can download the Power BI Designer
Head over to the Power BI blog to get all the good news for what's been added in this update.