Looks interesting. I'll have to try it out. I've always liked the idea of topic based messaging. That's basically what Twitter hashtags are.
How does one limit the audience of any particular message in a topic? Are messages just visible to everyone on the server? If it's federated do your messages propagate out forever?
It runs on a federated network where you connect with contacts. When you create a topic you can add or remove contacts to the topic. To your point about 'propagate out forever', there is no server-side replication; your contacts pull directly from your node. When you delete a topic, the data is deleted. Let me know if you have any issues getting the project to work, I am really eager for any kind of feedback.