Framelayout alternative in flutter

Stack is most likely what you want.

Stack allows to put widgets on the top of others however you like. And, combined with Positioned, have custom positions.

Let's draw a real frame in flutter :

Stack(
  alignment: Alignment.center,
  children: <Widget>[
    Container(
      width: 200.0,
      height: 300.0,
      decoration: BoxDecoration(
        color: Colors.black12,
        border: Border.all(
          color: Colors.black,
          width: 3.0,
        ),
      ),
    ),
    Container(
      width: 100.0,
      height: 100.0,
      color: Colors.blue,
    ),
    Positioned(
      bottom: 10.0,
      right: 10.0,
      child: Card(
        child: Padding(
          padding: const EdgeInsets.all(8.0),
          child: Text("Title"),
        ),
      ),
    )
  ],
),