I've found the following epw file parsers:

python

• Ladybug
• pyepw

javascript

• (EDIT): lmnarchitects (in page resources, need to open a DOM inspector to get to it)
• I made an epw2jsonone for a weather file visualization tool I'm working on: (https://www.dropbox.com/s/qvvxptplkan5g2f/epw2json.js?dl=0). script for epwvis.I'll post a github link once it's a bit more developed.

There are also some tools in the OpenStudio ruby SDK.

Haven't found any opensource C# or C++ ones yet. Seems pretty straightforward. Just reference the epw.idd.