Is there any app available similar to solo learn for machine learning, where I can challenge people

Answer 1

There is a good course in udacity for free. But there are no challenges like in here(Though there are some sort of assignments)

Answer 2

Unfortunately, none that I know of, however (and I know you aren't looking for this) there are a lot of competitions you can enroll in to win big prizes and verse other people. Still, I wish SoloLearn could implement that as a "weapon".

My preferences:
https://www.kaggle.com/competitions
https://www.quantopian.com/