Open Office - no, the other one
I think this is huge - Microsoft Office is switching to XML for many of it's default file formats. So now you'll be able to look inside a Word document, hell, now you'll be able to write a Word document!
Of course, this means that all the files will be much, much bigger, right? Nope, because they are actually zipped. Rename from .DOCX to .ZIP and you can open them and extract the XML file within. So files are actually about a 1/4 of the size of the current binary files!