Twitter is a free social networking and micro-blogging service that allows users to send updates (otherwise known as tweets) which are text-based posts of up to 140 characters in length.
Updates are displayed on the user’s profile page and delivered to other users who have signed up to receive them. The sender can restrict delivery to those in his or her circle of friends (delivery to everyone being the default). Users can receive updates via the Twitter website, instant messaging, SMS, RSS, email or through an application such as Twitterrific or Facebook.
Pownce is a free social networking and micro-blogging site started by Internet entrepreneurs Kevin Rose, Leah Culver, Daniel Burka. Pownce is centered around sharing messages, files, events, and links with already-established friends. The site launched on June 27, 2007, and was opened to the public on January 22, 2008.
tumblr is a tumblelog site. A tumblelog is a variation of a blog that favors short-form, mixed-media posts over the longer editorial posts frequently associated with blogging. Common post formats found on tumblelogs include links, photos, quotes, dialogues, and video. Unlike blogs, tumblelogs are frequently used to share the author’s creations, discoveries, or experiences while providing little or no commentary.
Jaiku is a social networking, micro-blogging and lifestreaming service comparable to Twitter. Jaiku was founded in February 2006 by Jyri Engeström and Petteri Koponen from Finland and launched in July of that year. It was purchased by Google on October 9, 2007.