The Semantic Web (Web 3.0)
Web 1.0 "The Original Web" was all about connecting people to information, the mostly read only web.
Web 2.0 "The Social Web" was all about getting people to connect with one another and establishing a presence for them on the web, the read write web. Now that you have gotten the chance to get to know each other through the web, it’s time for our computers to socialize.
The aim of the next iteration of the web, Web 3.0, "The Semantic Web" is that computers will be able to understand the content and the information they contain. Rather than the data just being a document, it will be put within context helping the computer to relate pieces of information and present them to you accordingly. Therefore, you will no longer have to sift through a pile of search results, some of which are irrelevant, to get the information you want.
The Semantic Web is a web that is able to describe things in a way that helps computers understand the meaning behind a page. This will lead to more precise and personalized responses.
The Semantic Web is not about links between web pages.
The Semantic Web describes the relationships between things (like A is a part of B and Y is a member of Z) and the properties of things (like size, weight, age, and price)
Here's an interesting blog "Kris 2.0 Web meets World " which further tries to delineate the differences between Web 1.0 Web 2.0 and Web 3.0
Evri ( A Semantic Real Time Discovery Engine)
As web content continues to explode, trying to filter through the clutter to find the information that really matters can be frustrating. Evri works as a discovery engine, delivering intelligent, real-time streams of information on topics that matter most at that moment: on the web and to the consumer. It uncovers the most popular and trending stories, enabling consumers to share and engage with the stories they are most passionate about - in a delightful and unexpected way
News360 ( A Semantic News Aggregator)
News360 uses semantic analysis to deliver the most relevant news of the day, including stories about your favorite topics from your favorite sources. The semantic underpinnings of the app, which works on iPad, Android, Windows Phone, the PlayBook and now the Web, are a key differentiator for this application. The semantic technology is used to better personalize your own news reading experience. There are around 700,000 different entities known to the News360 semantic engine, each person typically has 5 to 10 “persistent” interests. These interests are automatically discovered for you by the app, after delving into your social Web activity.To determine what these interests are, the app doesn’t just pull from one network, or one dataset, like your “likes” on Facebook, or your Twitter “favorites,” for example – it looks at everything…given permission, of course. In addition to Facebook likes, the app reads your Facebook profile data, sees what you comment and share and examines how you interact with content. On Twitter, it looks at your bio, your lists, your tweets and your favorites. On Google Reader, it knows what you share, what you star, what you read and what clicked through to. And on Evernote, it looks at which web clips you saved, especially those that are news-related.
Hakia (A Semantic Search Engine)
Hakia calls itself a “meaning-based (semantic) search engine.” They’re trying to provide search results based on meaning match, rather than by the popularity of search terms. The company uses something they call “QDEX,” which they claim analyzes Web pages better than indexing. Hakia also has a number of interesting features. For example, for short queries the site displays results in categories, instead of a standard list like you’re probably used to. For longer queries, Hakia highlights what it believes to be relevant phrases or sentences. Additionally, Hakia adds some social features to it’s search engine.
Wolfram Alpha ( A Direct Answer Search Engine)
It is not a search engine. A search engine gives you links; Wolfram Alpha gives you answers. It is the world's biggest calculator. Wolfram's Luc Barthelet puts it this way: "We do not search the Web. We do not search Web pages. What we do is answer the questions that people ask through a process that is similar to solving an equation."
Introduction to The Web 3.0