Which is the best CMS for mobile app backend?

I’m thinking of launching a new app. My app will need a backend. I wanted to know which cms will be best for this purpose? Is there any cms which is specifically designed for mobile app backend?

You are looking for wrong kind of system. You don’t need a CMS as such but you need a script/software which can create API which you can use for building mobile app. This system should also be able to serve as single point for all backend requirements. Unfortunately there is no such pre-built system available right now. You have to code your own or find a developer to build it for you.