Ask HN: What is something you did cool? Brag about it

Just for fun, because bragging is generally quite annoying. But here's your opportunity to go ahead and boast. The only criteria is that it should be true :) I will start. I made a successful transition in my previous company from a proprietary tool (IBM BPM tool) to a completely free an open source alternative. And features that were not supported by the open source tool but the project depended on, I implemented them myself. It was a 4 month personal project, but saved my employer $30000 a year after that. May be a small achievement, but I am proud about it.