Metadatics uses TagLib. TagLib is licensed under LGPL and MPL. The TagLib project can be found here: http://developer.kde.org/~wheeler/taglib.html
Metadatics uses libogg for dealing with files in an ogg container. Libogg is licensed under the Xiph.org BSD-Like license. Libogg source code can be found here: http://www.xiph.org/downloads/
Metadatics uses the HexFiend Framework for editing binary data in some tags. The Hexfiend Framework is licensed under the Two-Clause BSD License. The HexFiend project can be found here: http://ridiculousfish.com/hexfiend/
Metadatics uses GCUndoManager to handle undo and redo operations. The GCUndoManager project can be found here: http://apptree.net/gcundomanager.htm
For Mac App Store receipt validation: This product includes software developed by the OpenSSL Project for use in the OpenSSL Toolkit (http://www.openssl.org/). This product includes cryptographic software written by Eric Young (eay@cryptsoft.com).