I can only speak for myself, but I'm quite sure this goes for many of us: Instagram is perhaps the single most app that defined the smartphone as we know today.
It is the app that made mobile photography so popular, and accessible to so many people. People found new jobs, new lives, partners, discovered new countries, and made so many friends. Can you even imagine how it was before Instagram?
Thank you, @Instagram!
Feel free to like this if you feel the same.