As per Microsoft: a cloud-based business intelligence service that gives people a powerful new way to work with data in the tools they use every day, Excel and Office 365. With Excel you can now discover, analyze, and visualize data like never before to find valuable business insights. With Power BI for Office 365 you can easily deploy a cloud-based BI environment. Couple of features that I would like to mention here:
In order to understand the differences between Power BI and tableau: Please read the article below written by BI Expert Jen Underwood, very detailed analysis...