Viber vs Discord

Viber has native apps for both Windows and Mac that allow you to send and receive messages from your desktop. You can also use the desktop to make and receive calls. Synchronizes between all devices you are using Viber on. Allows transferring calls between devices.

Viber has really well implemented voice tech. It has comparable quality to Skype and you can even tranfer calls from your phone to your desktop seamlessly.

Viber uses data connection and the app is free.

The interface is simple, functional and intuitive.

Viber is tied to your phone number so it can quickly see who else in your contacts list is using the application.

Viber includes Android Wear support on Android 4.3 or higher and Viber 5.3 or higher.

Viber's protocol uses the same concepts of the "double ratchet" protocol used in Open Whisper Systems Signal application.

It's possible to be a fly on the wall on other group or one-to-one chats that have been opened up to the public. These public chats are often promotional chats with celebrities.

Can call friends using voice or video options.

This has an advantage in that if you text someone who uses Viber it will be free, if not it will just revert to SMS. This means you can replace your standard messaging app with Viber as well.

Starting with Viber 6.0 the encryption keys are stored only on the clients themselves, not even Viber itself has access to them.

One of the best things about Viber is how it handles setup and sending messages. Viber uses your existing number as your ID, so you don't need to create a separate Viber account.

Viber allows creating groups of up to 200 people on the Android version of Viber. It also has a cool "smart notifications" feature to prevent being overwhelmed with notifications if a lot of people are active in a chat group.

Viber has made a documentation available, explaining in great details their encryption system and giving good insight on how it works.

Discord follows the same type of interface design popularised by Slack, which is extremely clean and attractive, and doesn't clutter the interface with unnecessary chrome and cruft.

Unlimited amount of users.

Users can invite others to join a Discord channel via a web link, which means no installation is required to use the software - which is one of the big typical barriers to entry for social software.

Discord allows inviting people to a specific channel with a link. Links can be set to expire. Low effort/passive invite mechanics.

You can quickly send invites to people and they can join in using the web client without having to create an account or install the app.

Behaves and looks like Slack for regular text channels, but with the ability to create voice channels as well

Deny access, Deny write message, Allow read messages etc.

Discord provides an API for creating custom bots.

Discord has a wide variety of bots for things from airhorn noises to automated server management, to leveling systems for chat. The bot API is open and there are dedicated sites for finding bots.

Discord shows which game each user is currently playing, which among other things helps users to form PUGs with minimal hassle.

For those that are used to the way Slack (a similar chat client) works, Discord will be familiar in its use, which lowers the learning curve quite a bit for those that have switched or tried Slack before.

The support is limited but still exists. It's a killer feature for dev teams.

Discord prevents users from being DDoSed out of games.

Targeting roles allows for quickly requesting someone from a group e.g. artist, moderator, etc.

Ability to create channel categories for channels to sit inside of.

Free account have no tangible restrictions.
Premium account is just a way to say "thank you" to developers. And it work for all servers of discord (not as in slack). And it can be purchased by one who wants. In contrast to Slask, where all active members of the server should be "premium".

Have localization for many language, including Russian.