I think Duolingo is great! The app allows you to choose how much time you have to study each day, and sends daily email reminders so I can’t use the old “I forgot” as an excuse.

It has enabled me to study during my daily 1-hour commute to and from work. I’m not able to use the microphone option, so I’m not doing much of the talking to work on my pronunciation, but the rest works fine. I put on my headphones and go into study land whenever I am on the train.