Right on time, Microsoft Office 2016 is now available for Windows, following the Mac release from July. You can either get it as part of an Office 365 subscription, or you can go with a one-time purchase. The latter option has become available for Mac today as well, since up until this point you had to go the Office 365 route. The one-time price is $149.99 regardless of which OS you have.
Otherwise, Office 365 subscriptions start at $69.99 per year, and deliver continuous app updates as well as other integrated services such as Yammer, Delve, and Skype for Business.
Office 2016 comes with support for co-authoring, Skype in-app integration, and Office 365 Groups inside Outlook 2016. Additionally, Outlook 2016 has smart search, automatic removal of low-priority mail, and support for cloud-based attachments. Excel 2016 includes integrated publishing to Power BI, as well as new chart types. Throughout Office, there's a most recently used documents list which lets you quickly jump back in.