Groupy is very easy to use. The creators took care of the possibility of automatically grouping windows of one program into cards, presentation of thumbnails of windows after hovering over the card and dragging cards between the Group's windows.
To connect windows to a group, just drag one of them to the top of the other's border. The cards will be shown automatically. If you do not want the windows to be connected, just hold down Shift as you drag. You can also change the behavior of shortcuts and, for example, combine windows into groups only when the modifier key is pressed.
In the settings you can also change the colors of active and inactive cards and frames.
The program in the trial version works for 30 days. The full version costs $ 10, Groupy is also part of the Object Desktop package.