I use a browser and messaging apps every day for browsing and communicating with friends. They're the apps I always install when I change phones. Other useful apps to me are a map, banking apps, an authentificator and a SMS app. Map apps are very helpful when I travel around unfamiliar places. I use banking apps for checking and paying bills. For some reason, it is easier to log in via apps than from their websites. They send SMS codes to log in my account on their web page, but there's no need when using apps. Authentificator is required for PCs at work. So I just downloaded it. I sometimes need SMS texts for authentification purposes on some websites. My mobile is becoming an identification for online services more and more. And the must-have apps on it are increasing.