At vFlyer we very much see ourselves moving steadily towards a new paradigm of classified ad distribution, and as a result, many times we find ourselves labeled as a "Web 2.0" or "Classifieds 2.0" company. Earlier this year, I started to identify and understand how other companies, particularly in the real estate space, were extending or introducing new paradigms of their own. Sometimes it's convenient to try and divide companies (Web 2.0 companies in this case) into meaningful categories. For example, Pat Kitano talks about self-expression, relationships and collaboration in the Web 2.0 social networking space as potential groupings. This is my attempt to identify and communicate the functional categories that I think matter most to real estate professionals.

I am sure some of you are asking "What is Web 2.0?" Unfortunately, there is no one good definition, but to paraphrase the wikipedia: Web 2.0 is a term often applied to a perceived ongoing transition on the Web from a collection of static websites to a full-fledged computing platform serving web applications to end users. The companies I mention below are provided as representative examples only and are not necessarily comprehensive, but I thought I would share them with you:

Aggregation
	Real estate search engines and aggregators help buyers find homes for sale or rent by collecting (or aggregating) listings from multiple sources into a single location. By crawling, indexing and then conveniently organizing and mapping listings, aggregators simplify and speed up the search process for online buyers. Trulia and PropSmart focus on homes, while HotPads focuses on apartments and rentals and MyNextDeal on commercial properties.
Blogging
	Blogs originally started as personal journal sites but have evolved into powerful business tools. Real estate blogs allow real estate professionals to communicate local real estate information as well as share knowledge and opinions. Companies in this category enable agents to manage and promote their blogs. ActiveRain, the 800-pound gorilla in this category, does this in the context of a great real estate community, while Blogging Systems and RSS Pieces are blogging platforms and solution providers.
Community
	Real estate Communities allow real estate professionals to connect with each other on the Web. Second generation communities like ActiveRain allow users to collaborate and share information online through blogs, forums, and other forms of interactive communication. Others with an eye on building online real estate communities include Zillow, which has added Home Q&A as a community feature aimed at home buyers, owners, and sellers to its site, and is continuing to move in that direction. Inman's Real Estate Connect is perhaps where online real estate community started and still thrives.
Communication
	Communication offerings range from instant messaging (IM) service aggregators like Meebo to click-to-call service providers like Jaxtr and ZiffTalk. These services make it easier for prospective buyers to contact real estate professionals via IM, phone or email. Most have widgets that can be embedded on websites or blogs to facilitate the communication process.
Distribution
	Distributors and syndicators like vFlyer, enable real estate professionals and online sellers to distribute their listings and classified ads to leading online marketplaces like Google Base, Oodle, Vast, Trulia, Edgeio, Propsmart, Hotpads and others. Point2 also has distribution tools for property ads, but vFlyer supports significantly more "delivery endpoints" including email, widgets, mobile and PDFs for offline use.
Mapping
	The companies build value-added service on top of mapping technology to deliver innovative, interactive or unique information that is interesting or important to prospective home buyers. Zillow maps home valuations on satellite maps, Neighboroo visualizes area demographics using color-coded "Information Maps", Trulia uses "Heat Maps" to show pricing trends. Hotpads also uses heat maps to display census data for neighborhoods.
Reviews
	These sites either allow consumers (online buyers) to review or rate real estate agents or provide other metrics (such as homes sold, i.e.) to help home buyers find, evaluate and select a REALTOR®. Homethinking provides customer reviews, as well as current and past listings as indicators of performance. Realty Baron provides REALTORS with an AgentRankTM based on professional experience, recent home sales, and endorsements, while Incredible Agent provides a "unique rating system" designed to help "incredible agents" stand out.
Social Bookmarking
	Social bookmarking allows users to store, organize, share, search and most importantly rank bookmarks or links. Real Estate Voices is a real estate social bookmarking site that help users discover the most interesting articles of the day, as voted and suggested by fellow users, saving users time and exposing valuable knowledge quickly.
Social Networking
	Social networks build on community sites by highlighting individual user profiles, enabling and encouraging the adding of "friends," contacts or associates, and balancing user interaction with group interaction. InmanNews probably best describes their true potential when it says "Social Networking websites present new opportunities for real estate brokers to find and recruit new agents, or find fresh sales leads. New agents might find them useful for gleaning business advice from other agents. Home buyers and sellers could tap them as a resource to find a real estate agent." ActiveRain is the "MySpace of Real Estate," while MyBlogLog connects users through their blogs.
Widgets
	Widgets allow real estate professionals to embed elements of core functionality directly on their websites, social networking sites, or blogs by simply copying and pasting HTML code. vFlyer's listing widgets enable REALTORS® to list one or more properties for sale on their blogs, Trulia's TruliaMap shows all the listings in a given location and WidgetBox is a general marketplace for widgets with several interesting categories.
Wikis
	Wikis are a shared central source of knowledge and information that usually anyone can contribute to. By allowing contributors to collaborate and by combining knowledge from diverse resources, the goal of a real estate wiki is to become an authoritative source of real estate information. Zillow Wiki was one of the first, InmanWiki which aims to be the "world's largest real estate encyclopedia."
Valuation
	These companies allow consumers to get, provide or understand real estate property valuation information. Zillow, eppraisals.com and HomeGain provide property valuation information. My-currency.com provides community-driven price predictions for homes, while others like Altos Research provides real-time market trend analysis. For real estate professionals, these services can help provide a "pricing context" and comparables for prospective buyers and lead to more educated decision-making.
Video
	These companies provide services that allow real estate professionals and online sellers to upload, manage and host video tours or other business videos. YouTube simply provides hosting (and in some cases, marketing exposure), while others like TurnHere and WelcomeMat provide other value-added services, including the ability to locate videographers or help with product.

To give credit where credit is due, I did get some early input from Kevin Boer of 3 Oceans, Pat Kitano of Transparent Real Estate, and Erik Hersman of RealtyThoughts.

If you think I've missed a category, let me know. I will do a follow on posting with your ideas and suggestions. Hope you find this list useful (or at least interesting).