An important piece of Office news was buried in all the OneDrive and SharePoint announcements last night. Microsoft today launched Office Online Server (OOS), which essentially lets businesses host their own Word, Excel, PowerPoint, and OneNote apps.

Office Online, previously known as Office Web Apps, consists of lightweight Web versions of Microsoft Office applications. OOS is the successor to Office Web Apps Server 2013, and it can scale for your enterprise whether you have 100 employees or 100,000, Microsoft says.

Microsoft explains why OOS exists: “many organizations still value running server products on-premises for a variety of reasons” (namely, privacy and security concerns). OOS offers the same features as Office Online, just hosted in your own datacenter. The company further promised to deliver new Office Online features to OOS through regular updates, though it didn’t commit to a timeframe.

A single OOS farm can serve multiple SharePoint, Exchange, and Skype for Business instances. OOS is designed to work with SharePoint Server 2016, Exchange Server 2016, and Skype for Business Server 2016, but is also backwards compatible with SharePoint Server 2013, Exchange Server 2013, and Lync Server 2013. Other products can talk to OOS via Microsoft’s public APIs.

The good news is that OOS won’t cost your company anything more, assuming that you’re already an enterprise customer with Microsoft’s volume licensing. You can download OOS right now from the Volume License Servicing Center.

The bad news is that OOS has view-only functionality out-of-the-box, meaning it’s rather useless unless you pay more. For document creation, editing, and saving, you will need to have an on-premises Office suite license with Software Assurance or an Office 365 ProPlus subscription. Microsoft says customers that purchase an on-premises Office 2016 suite through Volume Licensing between now and August 1, 2016 will be exempt from the Software Assurance requirement through August 1, 2019.

In other words, you have three months to decide if OOS is worth your money.