Do you remember when technology blew your mind for the first time ever and kickstarted your tech ambition? For me it was the iPod Nano, I remember seeing the ad and being hooked on tech and especially music tech ever since.
I think it might be Norton Commander ("NC"). It was the first user interface I have seen as a kid when I just started using the computer. Till then it was only DOS commands
JPEG. When I first understood how the image compression algorithm works, I was fascinated about the signal processing technologies. So simple yet so powerful!