Viber

Pros: Works well as a desktop messaging app, synced with the android version. But the alternatives are much better, thus this is not to be recommended.

Cons: This software insists to interrupt you by its updates, which become available very frequently, and which you have no choice but to be interrupted by, since the app doesn't give up till you restart it, then opens up its blog page each time. There is no option to turn this incredibly annoying behaviour off. Irritated customers writing reviews such as this one, ensue.

Also, the advertising is very obtrusive.

Overall: Just use WhatsApp or other alternatives that equally have a desktop app for Windows/mac, they don't use advertising and don't interrupt you all the time with their stupid unnecessary updates.

Pros: (+) Viber desktop application and very good sync with the desktop application.
(+) Transfer of photos and videos without drop in quality.
(+) It can seamlessly do group calling with more users without a drop in quality.
(+) Self-erasing messages is a great way of cleaning up space.

Cons: (-) No blocking of calls feature.
(-) Nonavailability and limited audience base which is a drawback.
(-) Too many stickers and gifs make it annoying.
(-) There is no backup option for your chat like in WhatsApp.

Overall: I started using Viber in early 2015. I liked the desktop application which comes in handy. The application provides great video and audio calling quality. Images and videos can be shared with dropping quality. If you can convince people around you to use Viber it is a good option.

On an overall level, it is a really good option for day to day communication. It does the basic job and provides good features.

Pros: This was one of the first instant messaging app I had on my iPhone. Simple to set up and uses your phone number and instantly shows all other contacts that have Viber.

It has stickers which is a fun way to communicate with friends and family.

Great group calling support and quality with 20 people and more.

Has message encryption so your privacy is safe.

Cons: Needs more innovative features to catch up with its competitors.

App crashes sometimes and have to close the app via switcher and open again.

Sometimes doesn't detect mobile data.

Overall: It's a great app and I still use it because of the video call quality and security. Personally I find the stickers very appealing. But it has some rough edges and can do better.

Pros: It can connect more than 200 people in group chat. Video quality is very good even on unstable connection. Funny stickers and emojis. Can join many global public community to make new friends.

Cons: I never faced any issue on usage of this app. It works very well for what it made for.

Overall: Overall I'm using Viber for a very long time and can say it's best of any video calling app. It's very fun to use app. I liked its self destruct mode which automatically delete chat after your read no other app have this functionality.

Pros: Love how easy it is to use to send messages internationally at no additional cost when they also have Viber.

Cons: Super easy to use which I can't think of any cons.

Overall: It's such an easy tool to use and i'd recommend it for anyone needing a messaging tool for international use.