xvdtool is a C# command-line utility for manipulating Xbox One XVD/XVC packages. It can print detailed info about package headers, resign, rehash, en/decrypt and verify data integrity of a package, it can also convert decrypted XVD files to VHD or extract the filesystem itself.
So far it's only been tested with dev-crypted packages (which use a different 256-bit Offline Distribution Key (ODK) to retail packages), as the retail key is still unknown. This currently makes the tool useless for 90% of people, but developers looking into how XVD files work will find a detailed mapping of the XVD structures and near-complete methods for manipulating them.
However no encryption keys are provided with this tool, you'll have to find them yourself. Hashes for the dev keys are provided below. If you have an Xbox One development kit or GamingServices framework (Windows10-exclusive) installed, you can use DurangoKeyExtractor to extract the keys from there.
Also included is a tool for extracting files from the XBFS (Xbox Boot File System) inside the Xbox One NAND, based on tuxuser's original NANDOne work with a few small additions. Thanks Kebob for providing OpenXvd.