Preon is a framework for dealing with binary encoded data. It intends to be to binary encoded data what Hibernate is to relational databases, and JAXB to XML.
Instead of forcing you to write a decoder, an encoder and documentation, it allows you to define the mapping from the in memory data structure to its encoded representation once and only once, and get the decoder, the encoder and documentation for free.
Preon has been presented at Devoxx and OOPSLA. It originated at TomTom, the car navigation company, where it was used for decoding compressed map files.