Office Online Server Preview

Office Online Server (OOS) Preview is now available for download from Microsoft Download Center. This download is a standalone on-premises server, which provided browser-based versions of Word, PowerPoint, Excel and OneNote.

Detials
Use Office Online Server to provide browser-based file viewing and editing services for Office files. Office Online Server works with products and services that support WOPI, such as SharePoint Server 2016 Preview and Microsoft Exchange Server 2016. An Office Web Apps Server farm can provide services to multiple on-premises hosts, and you can scale out the farm as your organization's needs grow.

Office Online Server brings the features and improvements you experience with cloud-based Office Online to your on-premises solutions. Here is an overview of the updates and improvements:

• Improved co-authoring support
• Significant additions to authoring features
• Heavy investments in performance and stability

Download
The link in following website correspond to file available for this download. Once you click on the "Download" button, you will be prompted to select the files you need. Download the files appropriate for you.

• Office Online Server Technical Preview

System requirements
Supported operating systems:

• Windows Server 2012 and Windows Server 2012 R2

Office Online Server requires Microsoft .NET Framework 4.5.2

Office Online Server works with the following Office program:

• Internet Explore 11, Microsoft Edge, Apple Safari (Latest), Google Chrome (Latest), Mozilla Firefox (Latest) 

Source
Office Blog