Quote from the book "HSK 1 за 15 уроков + 5 пробных тестов"

Suitable for smartphones, Android tablets, e-readers (except Kindle) and many programs

Can be opened on almost any device

Can be opened on any computer

Can be opened on any computer

Suitable for Kindle e-readers and Android apps

Suitable for iOS devices (iPhone, iPad, iMac) and most reading apps

Perfect for iPhone and iPad

Development of FB2 format