Nintendo Entertainment System, back in 1986. :love-struck:
I had played games on Atari, C64 and others but the games were rarely good enough for me. I didn't know I could like video games that much until I tried the NES. I never forget the feeling of playing Zelda for the first time, or Metroid. No one else I knew had those games, and no internet or walkthroughs to spoil it with.
A piece of technology, yes, but it's not a PC..
As for operating systems I'd say Windows 7, because it's the only Windows version that just worked from day one for me. W8 is a close second. Those that came before usually needed a Service Pack before they got decent.
I'm using W10 now, I have nothing against the UI, but it could be more polished, and it wasn't very stable for me in the beginning. Oh and the settings/control panel is still a mess after all these years. MS started the transition away from the control panel 6 or 7 years ago, and it's still a mix of Modern, Vista and 95. Three styles from three decades.
I have absolutely nothing against Linux or OS X, I'm just not that used to them. If I had to payfor Windows I'd probably go for Linux instead.