Office Online Server (OOS) is the next generation of Office Web Apps Server (OWA), which allows organizations to deliver browser-based versions of Word, PowerPoint, Excel and OneNote, among other capabilities.
Office Web Apps Server is not supportable for Windows Server 2016.
Most people who need to run Office Online Server are having Skype for Business Server 2015/2019 or SharePoint. Within Skype for Business it will be used for PowerPoint presentations inside meetings.
You can download Office Online Server from MSDN or Volume Licensing Center. The latest version listed over there is November 2017(en_office_online_server_last_updated_november_2017_x64_dvd_100181876.iso). In the meanwhile there have been made some patches available that are solving a lot of issues.