https://github.com/JohnL4/HexGrid
A Java program I wrote to draw a hex grid and do hit-testing on hexes. I think it has an innovative approach to coordinate transformation using matrix math (change-of-basis matrices).
I'm not real proud of the code architecture (it's kind of hacky), but... it works. So far. :) Refactoring may eventually come, or I might switch to another language and/or architecture. Web app, maybe?