As a chemical engineer in the late 90's I used fltk to write a real-time photoresist film web inspection system. The first version in VB was too slow as the system used a laser to scan for defects in film going by at several hundred feet per minute. I was a novice C++ programmer and fltk was the only toolkit I could get my head around and came with a great UI builder (fluid). I even was able to write my own widgets. And all of this was running on a Celeron 300MHz system.