Learn Mandarin on LingQ

LingQ is a language learning app that uses the same logic for learning a new language as learning your native tongue: using content you already like. They have books, news, podcasts, sports coverage, politics, culture, and food to name a few.
Price: Free
Devices: Android, iPad, iPhone, and Web

Learn Mandarin on LuvLingua

LuvLingua is a language learning app that uses an interface that is more geared towards a younger audience. It's focused on vocabulary learning and listening skills. The basic app is free but the more advanced ones are paid.
Price: Free
Devices: Android, iPad, iPhone, and Web

Learn Mandarin on Fluenz

Fluenz is a language learning app that uses a video-based approach to teach users. Fluenz helps users build fluency (not pun intended) through various exercises which encourage retention of new vocabulary and grammar points.
Price: $408/month
Devices: Android, and iPhone

Learn Mandarin on Mosalingua

Mosalingua is a language learning system that prides itself in having 11 million learners. It works by using flashcards to teach you new words and phrases. The app also includes a pronunciation guide, grammar tips, and a dictionary.
Price: Free
Devices: