You can send bitcoin to any Bitcoin wallet for free with Bitstack.
To send bitcoin using the blockchain:
Navigate to the Wallet tab in your app
Tap on the Airplane button
Enter the amount of bitcoin you want to send
Scan a Bitcoin address QR code or enter a BTC address
You cannot yet receive bitcoin from any wallet using the blockchain (this feature will be available soon).
The minimum amount per transaction is 0.00006000 BTC or 6,000 sats (Satoshis).