In 2009 during my Masters I was taking a course in elliptic curves and I was having a tough time getting to grips with them. I discovered Sage and was suddenly (after an eight-hour compile time!) able to easily create and manipulate these objects in an interactive environment. It was mind-blowing! I ended up doing quite well in that module and I'd say that's largely due to William Stein's work.

I'm no longer in academia and haven't used Sage for years but it's great to see how far this project has come. I hope it gets the funding and development it needs.