Here's our list of ten cool companies or services that make use of real-time web in what they do. Most of the companies discussed below are already registered to attend the Real-Time Summit.

10. Search

There are many different real-time search engines that approach search in many different ways. People think that real time is just Twitter and sure enough, some of the search engines put Twitter search front and center. Few search only Twitter, though - there are only about 3 million links shared on Twitter each day.

Most real-time search companies believe that's not enough to power a full index and rely on other sources of additional links to look at, often from the click-streams of users who have downloaded their software and opted-in to exposing their online behavior anonymously. A combination of links from Twitter, other online sources and the clickstreams of users powers search engines like Wowd, OneRiot and Faroo.

9. Twitter as Trigger

Seattle startup Evri uses data from Twitter in a very interesting way. It watches for emerging trends on the site and when something is becoming a hot topic of conversation - Evri uses that as a trigger to prompt a query to other sources for information on the topic.

Patrick Swayze is being talked about a lot all the sudden on Twitter? Time then to ping mainstream news sources, image search and his Wikipedia page to check for updates. Evri then uses that updated information to build the topic pages it serves up in partnership with its publishing company customers.

8. Real-Time Publishing

Ted Roden, the founder of artsy social sharing site Enjoysthin.gs, says that ever since he started pushing new shared items live to the browsers of people on his site - the time people have spent on Enjoysthin.gs has jumped substantially. With an effective User Interface, a flowing river of news can be a very compelling way to consume content.

7. Real-Time Discovery

YourVersion and LazyFeed are two real-time discovery services that unearth blog posts, web pages and other resources about topics of interest to users. They are like broad, topical, personalized blogsearch with good spam control. These services are fun and useful. LazyFeed consumes both PubSubHubbub and RSSCloud feeds in real-time as part of its topical blog search and YourVersion won't disclose what technology it uses but says the company has been working on real time since before it was cool.

6. Real-Time Sharing

There are more companies online than you can shake a stick at that create a shared experience for remote users but one particularly interesting one is the just-launched Pip.io. Pip.io uses AJAX and XMPP to let users perform the communication functions of social networking (messaging, person to person sharing) through an "apps in the browser OS" metaphor. It includes presence information (your avatar glows green if you're online) and chat while doing things like watching YouTube or Netflix videos.

5. The Real-Time Web of People

Aardvark is a question and answer service that determines what topics you know about and who your friends are, then lets you ask the service questions. Those questions are routed to the most qualified people within two circles of your friends and the rate of prompt, satisfactory responses is the only thing that outdoes the glee-inspiring user experience by either Instant Messaging through a bot intermediary or on the company's new iPhone app.

Aardvark says that by knowing who in your extended social network is available at any given time, it can tap into social knowledge - the real-time web of people. Presence information is a key asset of the real-time web.

4. Real-Time Relationships (And Up-selling)

Olark is an XMPP system that puts a chat window on top of any webpage you publish and ties the communication with page visitors in to your favorite IM client. The system lets users do sales support for people who might otherwise leave a passive website upon having problems or unanswered questions.

3. Reputation and Issue Tracking

Many companies in the field of reputation and topic tracking are realizing that new publishing technologies warrant the creation of new listening technologies with faster response times. Discovering that a topic has been discussed online isn't difficult, but in the business world these discussions happen often enough that the real-time search has to be combined with rapid text, sentiment or conceptual analysis. "If you're looking at an individual story a human will beat a machine to death," says real-time text analysis service Lexalytics, "but on the aggregate a machine will do the same to a human."

Unusual grammar, deciding when a series of real-time blips constitute an event of interest and how to present a river of data for business users are all issues that real-time-savvy reputation tracking services wrestle with in building their products.

2. Pushing Financial Data

Real-time infrastructure company Kaazing uses HTML5 Websockets to push bits of financial data to web interfaces for banks. Many of those banks had been using only locally installed software in order to maintain secure persistent connections with a data source, now Kaazing helps them capture the benefits of applications on the web.

All kinds of data could be delivered in new ways using emerging push technologies. The most interesting use case we've heard of so far, though, may be a very big one that could take a long time to become reality.

1. Real-Time Push to Replace Web Crawling

PubSubHubbub co-creator Brad Fitzpatrick, a serial innovator who's been essential in the creation of social networking, OpenID and other technologies, says he thinks that real-time push technologies could someday replace the need for most of the web crawling his employer Google does to maintain its index. If all webpages were PubSubHubbub enabled, for example, they could simply tell a Hub about any changes they had published and Google could find out via that Hub. There would be no reason for Google to poll websites for changes over and over again.

Fitzpatrick says that when Facebook-acquired FriendFeed started consuming PubSubHubbub feeds for subscribing to Google Reader Shared Items, traffic from FriendFeed to Google fell by 85%.

That's a huge win for efficiency. So the real-time web could make the entire web a much leaner beast.

The web as synced-up, low-latency, highly efficient, presence-aware discovery, sharing and communication tool? That's just the beginning of the vision.

Come and join us to discuss these kinds of ideas and more at the ReadWrite Real-Time Web Summit on October 15th. If you can't make it in person, plan to watch selected sessions by live streaming video that day.

These are important developments with a whole lot of potential to change the way we use the web and what we can do with it.