My start up, Teethie, is working on building a new discussion platform - conversations on the web have so far been relegated to fairly linear paths, with threaded conversations being state of the art. However, that's not how we converse in real life, and building a tool that allows discussions to operate more naturally, and even, take advantage of the medium (i.e., unlike a face to face conversation, everything on the web is archived) in ways that enhance the conversation seem imperative to me if we're going to create a brighter future for long-form discussions on the web.
We are also primarily focused on communities, because I believe people don't want to talk to random other people, but rather people who are similarly engaged as them, and whom they have built rapport and trust with. I mean, it's ridiculous to me that we would call someone crazy if they walked down the street trying to strike up conversation with everyone they pass, and yet, we design our web products as if this was the way people want to behave.