Web-based applications and desktops
Ajax has prompted the development of websites that mimic desktop applications, such as word processing, the spreadsheet, and slide-show presentation. In 2006 Google, Inc. acquired one of the best-known sites of this broad class, Writely. WYSIWYG wiki and blogging sites replicate many features of PC authoring applications.
Several browser-based "operating systems" have emerged, including EyeOS and YouOS. Although coined as such, many of these services function less like a traditional operating system and more as an application platform. They mimic the user experience of desktop operating-systems, offering features and applications similar to a PC environment, and are able to run within any modern browser. However, these operating systems do not directly control the hardware on the client's computer.

Numerous web-based application services appeared during the dot-com bubble of 1997–2001 and then vanished, having failed to gain a critical mass of customers. In 2005, WebEx acquired one of the better-known of these, Intranets.com, for $45 million.

Internet applications
Rich Internet Applications (RIAs) are web 2.0 applications that have many of the characteristics of desktop applications and are typically delivered via a browser.

Distribution of Media
XML and RSS
Many regard syndication of site content as a Web 2.0 feature. Syndication uses standardized protocols to permit end-users to make use of a site's data in another context (such as another website, a browser plugin, or a separate desktop application). Protocols which permit syndication include RSS (really simple syndication, also known as web syndication), RDF (as in RSS 1.1), and Atom, all of them XML-based formats. Observers have started to refer to these technologies as web feeds.

Specialized protocols such as FOAF and XFN (both for social networking) extend the functionality of sites or permit end-users to interact without centralized websites.

Web APIs
Web 2.0 often uses machine-based interactions such as REST and SOAP. Servers often expose proprietary APIs (Application Programming Interfaces), but standard APIs (for example, for posting to a blog or notifying a blog update) have also come into use. Most communications through APIs involve XML or JSON payloads.

REST APIs, through their use of self-descriptive messages and hypermedia as the engine of application state, should be self describing once an entry URI is known. Web Services Description Language (WSDL) is the standard way of publishing a SOAP API and there are a range of web service specifications. EMML, or Enterprise Mashup Markup Language by the Open Mashup Alliance, is an XML markup language for creating enterprise mashups.