This openly-documented binary file format [1] is natively used by Igor Pro, by Wavemetrics Inc. Use of Igor Pro is recommended for viewing / use of data encoded in this format. The technical note at [1] provides C source code for alternative implementations to access this format.
References
[1] H. Rodstein, “Igor Pro Technical Note 003: Writing Packed Files,” WaveMetrics, Inc. (1999). Online: ftp://ftp.wavemetrics.com/mirror/IgorPro/Technical_Notes/PTN003.zip; accessed April 11, 2016