Great post thanks! I had only heard of Duolingo before reading this, so that was a great insight :-)
I had previously used Habit Bull to get on win streaks of daily habits, and I found that it helped BUT it wasn't quite as easily accessible as I would have liked in order to help more. I felt that if I could integrate it further into my phone then that would work better. Having said that, there is something simple and wonderful about checking off another success in a line of successes, and not wanting to break the streak :-)
I'm going to go check out a) what gamified apps I do have on my devices, and b) what other useful gamified apps there are that I might use.
I can't wait until there are tons of apps for every skill and every topic and they get more and more enjoyable and effective. I feel like the kids being born today at going to have college level educations before they reach high school and they'll actually enjoy the process.