If your usercount is sufficiently low (I don’t really know how many users you’d have to have for this to be infeasible, it really depends on exactly how interactive the app is going to be) you can always try Drab (ElixirForum thread). It’s in my mind one of the most pleasant ways to build an interactive app, provided your project allows for it. Being that it’s driven by the server it does put more load on it, though, so for apps where there’s a lot happening most of that won’t be offloaded to the client.
From what you’re describing, though, I’d think it’s definitely one of the better choices.
