I use Duolingo. I think its decent to build a base for a new language. I use the free version so I see the premium add daily which is fine. I find the amount of clicking through all the extra junk at the end of my lesson to be even more annoying than the add though. I feel like the designers are like "we created 100 features and we are going to show you every single one of them!" The end of my lesson goes like this. Watch our add > click. Look at your progress > Click. See your standing on the leader board > click. Open a chest to get a prize > click three times (for some reason). Open another chest > click three more times. Want to change your avatars clothes > click. Well done your on day 300! > click.

Its never ending. I just button mash at the end of my lesson to speed through all that endless annoying shit.

Other than that its good.