Finally the windows phone app.
There is no official release yet.
Known file limitations:
You can launch any associated app in Remote Files view through phone's Internet Explorer. Local files cannot be opened in Explorer (Security Setting).
Local files can be viewed by stripped down Internet Explorer-View if their are HTML or text-based files.
Image files should be accessible via Internet Explorer too.
Audio & media files could be opened via API call to build-in MediaPlayer (if the media type will be recognized).
Currently there is no possibility to open Office-based files or PDF-documents from local storage (remote files will work).
No chance to edit any file. A tiny text editor is planned but all other file types are a hard piece of work.
However for WP8 there will be so called "file and uri associations" which will enable some kind of communication between apps and make file extensions callable.