Identica, a Twitter-clone, was launched by the Canadian firm, Control Yourself Inc., yesterday. The software powering Identica is available with an open source license and it supports the OpenMicroBlogging spec. You can get the source code from: http://laconi.ca/

If you've looked a Plurk, another Twitter-clone launched in May '08, you probably wouldn't be too impressed. Plurk's interface is better than Twitter's and creates that 'Web 2.0' experience.