Evernote is a legendary note-taking app. It’s easy to use and comes with some really cool features including voice commands. You can also take a note and view it on your lock screen or smartwatch. Evernotes are also available across multiple devices, including on desktop. You can also find notes based on your location if you are near to where you took the note in the first place. There is a Plus version available for $2.99 a month and a Premium version for $5.99, but the free version is great as well.
There are a lot of apps out there that pay lip service to security and privacy, but Signal was built from the ground up with the goal of letting people easily communicate without having to worry about being overheard. The Signal app is a complete phone and SMS client replacement (though it works just fine as a standalone app, too) for sending and receiving encrypted calls and messages. A recent update has greatly improved the app's look and feel, proving that security and usability don't have to be at odds.
Microsoft Word is, simply put, the alpha and omega of word processing, and one of the key apps in Microsoft Office 365. You'll find it on every kind of computer in every kind of setting, and now it's available for free on Android. Word plugs into Microsoft's cloud infrastructure to keep your documents in order, but its main selling point is that this really is Word. What you make on your phone will look exactly the same on the desktop. For the worker on the go, it's essential. Android App