Free tweeter / miniblog

Jaiku - Jaiku allows you the ability to post “mini-blogs” which are short blogs (usually under 140 - 160 characters in length) about whatever you decide. Jaiku also allows you to link together content from other services and social sites that provide RSS/ATOM feeds and they can be displayed as well.
Twitter - Twitter lets you say what you are doing in 140 characters or less. Recently new features have been added that have made it into a great communication tool.