Office Web Apps is just the normal Office on a Web platform, the Office suite that has been "webified". Office Web Apps include Excel, OneNote, PowerPoint and Word. Web Apps provide users with a way to to view, edit, and share files right from a Web browser (Internet Explorer 7 or later for Windows; Safari 4 or later for Mac; and Firefox 3.5 or later for Windows, Mac, or Linux).
There are essentially three different versions of Office Web Apps. One version is free, which is an ad supported consumer version. Users can access this version through their Windows Live SkyDrive (25 GB of free online storage that you can access from anywhere with an internet connection), and / or through their Hotmail account. The other 2 versions of Office Web Apps are paid SharePoint-centric business versions. (one of these versions are hosted by Microsoft, and the other version are hosted by Microsoft's customers or Microsoft's partners)
You may think these changes are quite small, but the improvement these changes bring into Office Web Apps is very big. Just shows, small things does sometimes make a huge difference! Microsoft also rolled out an update to its Microsoft Docs service on August 24. Docs is a version of Office Web Apps that uses Facebook for sharing/collaboration. In addition to tweaking the overall look and feel, the FUSE Labs team that is working on Microsoft Docs added an option to tag documents with keywords, as well as a new search bar for searching by people, pages or tags, similar to how they can search today using Facebook.
Microsoft has finally added requested and some missing, direly needed features to Office Web Apps