Office Online (known before 2014 as Office Web Apps and as of July 2019 as Office) is an online office suite offered by Microsoft, which allows users to create and edit files using lightweight Microsoft Office web apps: Word, Excel, PowerPoint and OneNote. The offering also includes Outlook.com, People, Calendar and OneDrive, all of which are accessible from a unified app switcher. Users can install the on-premises version of this service, called Office Online Server, in private clouds in conjunction with SharePoint, Microsoft Exchange Server and Microsoft Lync Server.
Office Web Apps was first revealed on October 2008 at PDC 2008 in Los Angeles . Chris Capossela, senior vice president of Microsoft business division, introduced Office Web Apps as lightweight versions of Word, Excel, PowerPoint and OneNote that allow people to create, edit and collaborate on Office documents through a web browser. According to Capossela, Office Web Apps was to become available as a part of Office Live Workspace. Office Web Apps was announced to be powered by AJAX as well as Silverlight; however, the latter is optional and its availability will only "enhance the user experience, resulting in sharper images and improved rendering."  Microsoft's Business Division President Stephen Elop stated during PDC 2008 that "a technology preview of Office Web Apps would become available later in 2008". However, the Technical Preview of Office Web Apps was not released until 2009.
On July 13, 2009, Microsoft announced at its Worldwide Partners Conference 2009 in New Orleans that Microsoft Office 2010 reached its "Technical Preview" development milestone and features of Office Web Apps were demonstrated to the public for the first time. Additionally, Microsoft announced that Office Web Apps would be made available to consumers online and free of charge, while Microsoft Software Assurance customers will have the option of running them on premises. Office 2010 beta testers were not given access to Office Web Apps at this date, and it was announced that it would be available for testers during August 2009. However, in August 2009, a Microsoft spokesperson stated that there had been a delay in the release of Office Web Apps Technical Preview and it would not be available by the end of August.
Microsoft officially released the Technical Preview of Office Web Apps on September 17, 2009. Office Web Apps was made available to selected testers via its OneDrive (at the time Skydrive) service. The final version of Office Web Apps was made available to the public via Windows Live Office on June 7, 2010.
On October 22, 2012, Microsoft announced the release of new features including co-authoring, performance improvements and touch support.
In February 2014, Office Web Apps were re-branded Office Online and incorporated into other Microsoft web services, including Calendar, OneDrive, Outlook.com, and People. Microsoft had previously attempted to unify its online services suite (including Microsoft Passport, Hotmail, MSN Messenger, and later SkyDrive) under a brand known as Windows Live, first launched in 2005. However, with the impending launch of Windows 8 and its increased use of cloud services, Microsoft dropped the Windows Live brand to emphasize that these services would now be built directly into Windows and not merely be a "bolted on" add-on. Critics had criticized the Windows Live brand for having no clear vision, as it was being applied to an increasingly broad array of unrelated services. At the same time, Windows Live Hotmail was re-launched as Outlook.com (sharing its name with the Microsoft Outlook personal information manager).
In July 2019, Microsoft announced that they were retiring the "Online" branding for Office Online. The product is now Office, and may be referred to as "Office for the web" or "Office in a browser".
Word, Excel, and PowerPoint on the web can all natively open, edit, and save Office Open XML files (docx, xlsx, pptx) as well as OpenDocument files (odt, ods, odp). They can also open the older Office file formats (doc, xls, ppt), but will be converted to the newer Open XML formats if the user wishes to edit them online. Other formats cannot be opened in the browser apps, such as CSV in Excel or HTML in Word, nor can Office files that are encrypted with a password be opened. Files with macros can be opened in the browser apps, but the macros cannot be accessed or executed. Starting on July 2013, Word can render PDF documents or convert them to Microsoft Word documents, although the formatting of the document may deviate from the original. Since November 2013, the apps have supported real-time co-authoring and autosaving files.
Office on the web lacks a number of the advanced features present in the full desktop versions of Office, including lacking the programs Access and Publisher entirely. However, users are able to select the command "Open in Desktop App" that brings up the document in the desktop version of Office on their computer or device to utilize the advanced features there.
Word on the web lacks some Ribbon tabs, such as Design and Mailings. Mailings allows users to print envelopes and labels, and manage mail merge printing of Word documents. Word on the web is not able to edit certain objects, such as equations, shapes, text boxes, or drawings, but a placeholder may be present in the document. Certain advanced features like table sorting or columns will not be displayed but are preserved as they were in the document. Other views available in the Word desktop app (Outline, Draft, Web Layout, and Full Screen Reading) are not available, nor are side-by-side viewing, split windows, and the ruler.
Excel on the web can display most of the features available in the desktop versions of Excel, although it may not be able to insert or edit them. Certain data connections are not accessible on Excel on the web, including with charts that may use these external connections. Excel on the web also cannot display legacy features, such as Excel 4.0 macros or Excel 5.0 dialog sheets. There are also small differences between how some of the Excel functions work.
PowerPoint on the web does not support inserting or editing charts, equations, or audio or video stored on your PC, but they are all displayed in the presentation if they were added in using a desktop app. Some elements, like WordArt effects or more advanced animations and transitions, are not displayed at all, although they are preserved in the document. PowerPoint on the web also lacks the Outline, Master, Slide Sorter, and Presenter views present in the desktop app, as well as having limited printing options.
Supported web browsers include Microsoft Edge, Internet Explorer 11, the latest versions of Firefox or Google Chrome, as well as Safari for OS X 10.8 or later.
The Personal edition of Office Online is available to the general public free of charge with a Microsoft account through the Office.com website, which superseded SkyDrive (now OneDrive) and Office Live Workspace. Enterprise-managed versions are available through Office 365. In February 2013, the ability to view and edit files on SkyDrive without signing in was added. The service can also be installed privately in enterprise environments as a SharePoint app, or through Office Web Apps Server. Microsoft also offers other web apps in the Office suite, such as the Outlook Web App (formerly Outlook Web Access), Lync Web App (formerly Office Communicator Web Access), Project Web App (formerly Project Web Access). Additionally, Microsoft offers a service under the name of Online Doc Viewer to view Office documents on a website via Office Online.