This app is primarily used for reading content, although there are other features. As you read, you can mark words as known and see the total number of words you know. You can also read eBooks on the app, and import content from the web. I have mixed feelings regarding LingQ – on one hand, they offer a lot of interesting content at various difficulty levels, but on the other hand, I feel like they try to do too much and lack focus. Read the full review of LingQ.