This Friday, the collaborative web editor EtherPad finally shuts down. I first wrote about this editor in 2008. It was bought by Google last year (to add its developers to the Google Wave team) and temporarily taken offline, but after an outcry brought back pending the open release of its source code (which happened a couple of weeks later).
Since then, a number of EtherPad clones have sprung up—some using the source code with no changes, others extending it to add new features. Some are free and noncommercial, while others cost money to use. CNet has a good roundup of six of the more promising-looking EtherPad clones (though I take issue with their suggestion that Google Wave and Docs are somehow just as useful!), and a more complete list of EtherPad alternatives is on EtherPad.org (with an HTML echo).
Needless to say, those who have documents stored on EtherPad had best export them to their local computers—when EtherPad goes down, the stored documents go with it.
For my own EtherPad needs, I will be moving to iEtherPad—it implements the original EtherPad system, for free, but adds some additional formatting options such as font size and super/subscripting.