"Real-time web" is a new trend that is becoming more and more hype among search engines and various website services. First let’s define real-time web so we can understand better why it is so popular and then we will see a few popular real-time platforms.
According to Wikipedia:
The real-time web is a set of technologies and practices which enable users to receive information as soon as it is published by its authors, rather than requiring that they or their software check a source periodically for updates. The most successful examples are Facebook's newsfeed and Twitter.
If you get instant updates on Facebook or Twitter on whereabouts of your friends, why not being able to do that with search engines like Google and Bing. ReadWriteWeb has looked into this more thoroughly.
Among the most popular Real-time web platforms are Pubsubhubbub (delivers updates from a server out to all subscribers that have requested updates); RSSCloud ( similar but doesnt deliver full content); Tornado ( powers FriendFeed, offers a possible way to add real-time flow to applications) and Aardvark( get answers to questions from your extended social network). Read Write Web has the details.
In another post we will see how search engines are trying to implement real-time web.