The other day I came across this this post : it's a proof of concept of a real time collaborative spreadsheet that uses just open source technology. The idea is to make two spreadsheets talk to each other via telepathy protocol; this way two or more person can work on the same spreadsheet and share the ongoing modification by only being on each other telepathy list.
This video shows the proof of concept in action.
This proof-of-concept comes to you courtesy of Eike Rathke of Red Hat, Michael Meeks of SUSE, and Will Thompson of Collabora.
What else can I say other than " looking forward to see it in action " on my box !