It's an obvious and boring cliché, but I can't dispute the usage data on my phone which shows Twitter as being the most-used app by a long way. It's a good example of the UX being all about the content. Twitter's made such a huge impact over the last decade, and I'm privileged to have helped shape that in a very small way while I was there.
It sounds really boring – but I love Tesco's mobile app. It does what it should do, in a really easy way. As a busy working mother, I get to do my weekly shop in 15 minutes on my way home from work. What's not to love?