Docwit solves the problem where you want to use a collaborative web-based document system, but you don't want an external company (like Google or Adobe) to host your data.
We've used one of the most popular open source HTML wysiwyg editor components (TinyMCE), an open-source diff/patch library that Google happen to use (google-diff-match-patch), and some custom code to produce a light, cheap (effort-wise, free cost-wise) kind of collaborative editor. It's intended to be something simple that can be combined into your existing systems. For example, an early intended use is with the Sakai 3 courseware management system. However, the webapp package can just be run as a server itself so you can see it in action.
We currently use Jackrabbit for storage, but other storage mechanisms can be added.
A proof of concept alpha has been checked into the source code repository. It is a long way from being finished, but it can be built and run using Apache Maven 2. Technically-minded people can build and run using the following command line commands (assuming Java and Maven are installed):
mvn installin docwit-core (to download required libraries and compile the core code)
mvn jetty:run-warin docwit-webapp (to download required libraries for the webapp, build the webapp, package, and run it).
http://localhost:8080/docwit-webappto access it.
For the non-technically minded: things will gradually improve. "Alpha" means "not ready yet".