Ask HN: What apps/software do you love?

I was having an interesting discussion on growth yesterday with a friend and he said something that really resonated with me:

"Growth hacks are catalysts, not determinants. If your product sucks, they won't help. Users will just churn out, or worse, never even come back. If you build a product users love however, they will work like a charm."

Then the discussion turned to what defines loving a product. And we agreed a good proxy was when a user wants to pay for it.

So I ask the HN community - what apps/software do you love so much that you're currently paying for them? Or would pay for them if they existed?