Identica is a commercial offering based on the StatusNet package.

StatusNet is an open source microblogging server implementation formerly known as Laconica. What a name. That's probably why it changed.

It's most important feature is the ability to allow for decentralized microblogging - that means, having a federated interserver protocol to inform remote subscribers of microblog messages.

Currently the data is shared using so-called OpenMicroBlogging which means throwing all kinds of HTTP requests around (OpenID, OAuth: things that sit on top of HTTP, just as the IETF wouldn't have wanted it to be). A strategy which is known to scale really well... NOT!

It is being considered to upgrade to XMPP, which means it will still not have a high scalability model, but a lot better than what it has now.

Cross-publishing microblogs from psyced to StatusNet

Since StatusNet offers a Twitter-compatible API (See [1]) you can use psyced's OAuth capabilities also to publish your PSYC microblogs to Identica and other servers running StatusNet software.