If you ask me? Mobile/WiFi internet… The way and amount of time we use our phones had changed A LOT since their diffusion. I guess the release of the iPhone changed our idea of what a phone is too
Edit: when I say modern world I’m referring to the last 50 years. So stuff like “the electricity” or “the telephone” doesn’t count.
I read that washing machines had a big impact, manual washing of clothes could take a full day of work.
Glad to see someone has mentioned this. Huge gains in time in the day for a huge part of the population.