Pick your language:

• java: jmzml - https://code.google.com/p/jmzml/ (there are more java libraries out there)
• C++: proteowizard - http://proteowizard.sourceforge.net/
• R (based on proteowizard): mzR - http://bioconductor.org/packages/release/bioc/html/mzR.html
• python: pyteomics - http://packages.python.org/pyteomics

This is not an exhaustive list.

in case you are still looking for one.

• PDV: an integrative proteomics data viewer (https://academic.oup.com/bioinformatics/advance-article/doi/10.1093/bioinformatics/bty770/5087714)