We provide an Operational Transformation Engine at www.beweevee.com that works in web applications through either a Silverlight/Javascript bridge or natively. As an example, a client of ours has integrated their javascript text editing control using Silverlight only for OT transformation purposes as their backend was entirely coded in Java.
beWeeVee Notepad is a techdemo but it works. It does more or less the same as Etherpad. It also have an SDK to develop applications on top of the Operational Transformation Technology.
You can get more info at www.beweevee.com