Not exactly an App but I really enjoy the functionality that Samsung Dex brings.
It allows you to plug your phone into a desktop, monitor or lapdock (screen, keyboard/trackpad + battery) and give you a desktop like experience for when you need it. Plus each time you upgrade your phone you also get an upgrade to your laptop/desktop.
It does indeed have a bit of jank to it, but the functionality you gain is well worth it at least for me.