I'm looking for a software where many (~10) users in a LAN can look at and modify a document (text or whiteboard) at the same time. The software has to work without an internet connection, so it should not be a web service. It also should work without a server, but decentralized, so any user should be able to leave at any time without data loss. For lookup, it can use Broad- or Multicast.
I'm not interessted in using the software, but if there actually is something like that, and how good it would work in practice, so the platform doesn't matter. According to wikipedia, I'm looking for a data conferencing tool.