It was recently reported that Corel lost a patent lawsuit regarding the "fluent UI", or ribbon design, which resulted in Microsoft being awarded a total of $278,000 in damages. This is the UI that you see in MS Office products that replaces the traditional menu + toolbar design popular since the 1990s.

In 2005, Microsoft unveiled the Ribbon as its new user interface. At the time, Jensen Harris explained the reasoning behind the new UI in Why the UI, Part 1 and Part 2. Over the years he wrote many more posts on the Office 2007 UI.

The Ribbon UI was officially released in Office 2007 with Word, Excel, Access and PowerPoint. (In later versions other Office products would adopt the UI design.) Around the same time, they also announced a patent license agreement. This agreement included detailed instructions on how to construct the UI, down to the amount of spacing between each button. Developers who accepted this license had to agree to follow the current and future design guidelines closely and couldn’t make products that directly competed with MS Office. At the time there were concerns about accepting the license and many developers refused to sign it despite preferring to use the new design. There were also claims of prior art.

Since then the licensing agreement has been retired and all links to the Office UI license point to a blank page. With the Corel lawsuit, this has left many developers in a state of confusion. While desktop applications are far less popular than they were before, they are still being built and often developers choose a Ribbon-like UI to better match Windows applications such as Windows Explorer and Paint.

An anonymous user on StackExchange Law did discover a support page from 2013 in the Internet Archive. This is no longer available on the Microsoft site so it is unclear if this is still considered valid. Here is the text in its entirety.

The Office UI licensing program, originally launched in November 2006, has been retired. When the program was introduced in 2006, developer frameworks for the Office Ribbon did not exist. Microsoft tools and technologies now provide developers a variety of options, code, and developer frameworks for implementing the Office Ribbon UI in Windows applications. If you are a developer that already signed up for the Office UI licensing program and accepted the licensing terms, then you will continue to have rights under that license to implement the Office UI per the terms of that license. There are no changes at all for existing Office UI program licensees. If you are not already licensed to use the Office UI under the retired program, you can use any of the Microsoft tools and frameworks to implement the Ribbon UI in your current or future Windows applications. The license terms associated with the Microsoft developer framework will apply. For example, current developer frameworks that are licensed for creating a Ribbon UI include: Microsoft Ribbon for Windows Presentation Foundation (WPF)

Windows Ribbon Framework

Microsoft Windows SDK for Windows 7 and the .NET Framework 4

Ribbon Extensibility Overview

Microsoft Foundation Class Ribbon Component (The MFC ribbon may now be used under the same license as the Microsoft Windows SDK). If you are not already licensed under the Office UI licensing program, and you do not want to use any of the Microsoft tools and technologies, Microsoft no longer has a separate Office Ribbon UI licensing program. If you have any questions about the retired licensing program, please email the officeui@microsoft.com email alias.

The 2010 version of the Microsoft Ribbon for WPF control is still available along with instructions on its use. There are also numerous Ribbon libraries offered on NuGet whose status is now drawn into question.

InfoQ has contacted Microsoft’s legal department for further clarifications on this story and will be updating it as more information becomes available.