Here's another application that is able to take advantage of the Office Open XML formats. MindManager is able to transform "mind maps" into the Open XML format. This is really cool: http://channel9.msdn.com/ShowPost.aspx?PostID=235048
Doug Mahugh was telling me about this a couple weeks ago, but it's the first time I've been able to watch the demo. It's a great example of using the Open XML Formats as a communication format between two completely different types of applications. MindManager is a product from MindJet that is used for creating "mind maps."
Basically, they leverage XSLT to transform data from their application into wordprocessingML. So you can take any mind map you've created, and turn it into a wordprocessing document. You can also go the other way, so if you add some more headings to the wordprocessing document, when you bring it back into MindManager they will be transformed into new nodes in your map.
The reason they wanted to build this solution was that they wanted an easy way to collaborate on a mind map using common tools. Since they can't count on everyone having MindManager, they wanted to put the map into a format that was more interoperable. WordprocessingML is becoming an international standard, it will be supported by Word 2000, XP, 2003, and 2007. Corel has already said that WordPerfect would support it. Apple and Novell are on the Ecma committee standardizing the formats so you can probably expect something from them. Because of this, for the MindJet folks, it makes a lot of sense to build the translation to and from WordprocessingML so that more people can collaborate on the mind maps. They still feel that MindManager is the ultimate tool for editing a map, but there is now another alternative for folks that don't have it.
These were the kinds of scenarios that motivated us to move into the XML formats back at the beginning of Office 2003. We wanted to make Office a more valuable platform for building solutions, and opening up the file formats is a key component of that. We're now on the verge of a whole new world of solutions where people can leverage the power of Office on the client and the openness of the file formats on the server or any number non-Office applications.