Basically, SG Project Pro has an intuitive interface, multiple ongoin projects, linking with MS Project, Very good reporting features, Gantt timeline, action list, batch email to all contractors, and risk management. If there is one like that for Android, I'd be ecstatic.
It doesn't need to be free. SG costs 40 bucks and is worth every penny and more. I don't mind spending the money for a well made one, keyword being well made, at least on par with SG Project Pro.