Web 2.0
A blog (a contraction of the term "Web log") is a Web site, usually maintained by an individual with regular entries of commentary, descriptions of events, or other material such as graphics or video. Entries are commonly displayed in reverse-chronological order. "Blog" can also be used as a verb, meaning to maintain or add content to a blog.
A wiki is a page or collection of Web pages designed to enable anyone who accesses it to contribute or modify content, using a simplified markup language. Wikis are often used to create collaborative websites and to power community websites. The collaborative encyclopedia Wikipedia is one of the best-known wikis.Wikis are used in business to provide intranets and Knowledge Management systems. Ward Cunningham, developer of the first wiki software, WikiWikiWeb, originally described it as "the simplest online database that could possibly work".

Flickr is an image and video hosting website, web services suite, and online community platform. It was one of the earliest Web 2.0 applications. In addition to being a popular Web site for users to share personal photographs, the service is widely used by bloggers as a photo repository. Its popularity has been fueled by its organization tools, which allow photos to be tagged and browsed by folksonomic. As of November 2007[update], it claims to host more than 2 billion images.

Twitter is a free social networking and micro-blogging service that allows its users to send and read other users' updates (otherwise known as tweets), which are text-based posts of up to 140 characters in length.
http://www.bigthink.com/science-technology/10370

Seesmic provides anyone with a new way to communicate and connect online through threaded
video conversation. See and hear people share their experiences straight from their webcams and mobile phones, join in active conversations, and engage in real interactions with real
people.
The Seesmic platform also enables video conversations on more than a thousand sites, blogs and broadcasts them to other social software such as Twitter and Friendfeed thanks to its robust API.
Seesmic also operates twhirl, a social desktop client, that now enables Seesmic video comments. twhirl represents 12% of Twitter messages being sent and has over 400,000 downloads.
Video Blogging Class

