With text messages, audio clips, regular calls and video calls, Viber has the most options in a third-party messaging app.
With Viber you can send audio clips, locations, stickers, and emoticons with your text messages.
You get a good selection of stickers for free, but you can also buy themed packs for $1.99 through in app purchase.
The contact list is synced with your phone so you can contact anyone, but they will need to have Viber too if you want to make free audio or video calls or send text messages.
The call screen is much like what you have on your phone with all the features you need like speaker, mute and others.
You can explore the current public chats and watch the participants converse, but you won't be able to join in. Viber says that's coming in a future update.