I'm an Android phone lover, so I use all of these apps on my Samsung Galaxy S5. But, they're all available on Apple products, too.
1. Google - Having an Android phone, using the Google app as a widget on my home screen keeps me in the loop with everything in my life. Travel plans are automatically shown to me (with up-to-date info for my flights), scores for my favorite sports teams, tracking info for packages, and events on my calendar.
2. IF - This app is awesome! It connects all of my most important apps -- Instagram, Google Photos, Gmail, OneDrive, and tons more. You choose "recipes" to have IF watch for and trigger the app to work for you. I currently have recipes set up for my Instagram photos to be automatically backed up in my OneDrive, for Facebook photos I'm tagged in to by saved to my OneDrive, and to receive an alert the day before rain is in the forecast. There are so many cool ways to use this app! I suggest you check it out!
3. OneDrive - I love this app mostly because I'm a PC (and Windows 8) user. All of my files on my laptop are automatically synced to the OneDrive cloud and can be accessed on all of my devices. I can access files directly on my phone, when I need something on the go and my files are synced (with changes made!) between my desktop PC and laptop. OneDrive also saved my life once. No lie. My laptop died and I had all of my photos, TPT files, etc. on my laptop -- but luckily I had everything backed up! Thank goodness, or else I would have been out of luck! I absolutely LOVE it!