Google Hangouts supports everything that you would expect from a good messaging app. It allows you to use multiple Google accounts at the same time, and you can switch with one simple tap. Included is everything from video to audio calling, as well as instant messaging. You can easily attach pictures or other media. Download Hangouts, as a great alternative to Skype or Facetime.
Hangouts supports multiple accounts, you can log in with multiple Google accounts and if one account has messages you get a visible notification.
You can simply switch back and forth between accounts by tapping on your profile picture in the top-left hand corner of the app.
This makes it super easy to handle multiple profiles, for example one for business and one personal or maybe you like to have a family only account like me.
As Hangouts is a Google app it can be expected that it's integrated into other Google services, such as Google Voice. The integration works nicely, you can simply connect your Google Voice account and are then able to use Hangouts also for sending real SMS messages, as well as making phone calls just like you would with your phone.
Also the voicemail functionality of Google Voice is integrated into hangouts and can be used from inside the app.
Hangouts doesn't have a real desktop client, like for example Skype or Facetime. But it does have a web chat, which is integrated into Gmail and also accessible on it's own when you go to https://hangouts.google.com.
If you're logged into your Google account, you will see a beautifully designed chat UI, with shortcuts to make video & phone calls as well as sending messages (and SMS).
You'll find your existing chats & contacts on the left side. There is a little known feature that lets you use a chat in a little window that always stays on top, pretty much like a desktop chat would behave. To open this window, first you have to open a chat by clicking on it, then look at the top of the chat window and click on the arrow symbol. Now your chat is in it's own little window that you can drag around your screen and position it just like you would with a desktop software.
Hangouts in many aspects, is better than Skype in my humble opinion at least. It supports everything you know from Skype and other communication apps like for example Facetime. With an integrated Google Voice account it pretty much has the exact same feature set.
It is easy to use and integrates fully into Gmail. The only drawback I can find, is the lack of a real desktop client that you can install like Skype, Facetime and so forth.