Bird
With Bird we can declaratively specify how to parse binary data. This is how the PNG format is defined in Bird:
As we can see, some of Bird's most distinctive features are:
• Data Structure = Parser
• Primitive datatypes for tokens
• Annotations to provide context (e.g.: encoding, endianness)
The Bird project is open source and available at 
SWAT-engineering/bird.
For more information, see the Bird Language manual