Etherpad + plugins and many other extensions (check out the various branches). I'm available for consultancy hacking on etherpad.
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Pull request Compare This branch is 11 commits ahead, 15 commits behind ether:master.
Latest commit f5858f4 Jan 16, 2012 Egil Möller Merge pull request #1 from elrik/master
Here is the fix for the copyPad plugin