Ask HN: What was the most satisfying technical issue you solved?

It doesn't have to something complicated, but rather something sweet, that leaves a taste so sweet that it shies honey away.

Starting: Some 4 years back, I worked at a place which did not let engineers use internet. So while constrained to MSDN documentation, I was not even able to communicate with fellow engineers across the table because, well looks odd to jump around the office. So I developed this simple chat utility in VB for the three of us. That was sweet.

What about you?