I have found this deal somewhere online. 
So Rosetta Stone it's a Language Subscription   App. On the app it says that it costs $$. But there is a way to get it for one language for free.
How to get the freebie
- Optional for Android — Download App for mobile use 
 First download the app
 Note: Don't sign up or anything. Just download the app.
- Access free offer page 
 Go to this website and scroll until you find Rosetta Stone. Click on the + and then click on the Visit Rosetta Stone.
- Sign up & choose language 
 Then put an email where it writes Username, enter a password and choose one of the language of your choice.
 Note:- Choose wisely the language. You can only choose one. And you can not change the language.
 Click on the Sign in.
- Optional for iOS — Download App for mobile use** 
 Download the iOS app
 Reported to work by Flyingdoc
- Go to Rosetta Stone 
 Click on the Launch Rosetta Stone Foundation
- Start learning 
 The web learning portal / app will open. Sign in with the same Email and Password (if required) and you are ready to enjoy the freebie. No payment information required.
- Optional for Web — Revisit learning portal 
 Log in from here to revisit web learning portal.
Edit: "You may study more than one language. Switching from one language to another language must be performed only on this page." Thanks to @BigLeviathan.
Enjoy!!

 
    







Agree. Not better but complimentary.
Doesn't replace Duolingo for me