Twitter allows you to send short messages to your community of followers. You simply set up a free account and people can sign up to receive your messages - or tweets as they are known. Amongst people who live and breath the internet, Twitter is huge. It is not the best tool (try Pownce and Jaiku), but becasue it has the largest number of followers it is the one that everyone uses. - Read more

Delicious is a Social Bookmarking service, which means you can save all your bookmarks online, share them with other people, and see what other people are bookmarking. 

It also means that we can show you the most popular bookmarks being saved right now across many areas of interest. In addition, Delicious search and tagging tools help you keep track of your entire bookmark collection and find new bookmarks from people like you. - Read more

Swurl is a 'lifestreaming service', which brings all your web content (such as Twitter feeds and Delicious bookmarks, for example) together into a blog format, supporting your existing blog, pictures, links, videos, and more.

Swurl encourages conversations, not just comments. Swurl conversations are easy to write, read, and watch. You can also find your friends on other sites and automatically get a feed of their activity. - Read more