Piggy is completely free for making Investments in Direct Plans for any mutual fund. There are no charges for onetime investment, SIPs, Switch, STP, Redemption or tracking your existing investments.
There is no annual maintenance fees of any kind as well for your transactions. Also since all Investments are in Direct Plans of mutual funds, there is no money lost to commissions. You make up to 1% more returns on your investments over other trading, bank platforms and 'free' apps.