Stop a game from opening in full screen mode, with DxWnd
DxWnd is a portable and free program you may find convenient in case that you prefer to open a game or app inside a smaller window instead of letting it occupy the whole screen.
When you run DxWnd it opens a window that waits for your input: just drag and drop on this window the executable of your game or app and it will not open in full screen mode. Note that not all programs or games will obey.
DxWnd lets you configure its position and size. You can ensure optimum performance by configuring the Video, Direct3D, DirectX, Hook, Registry or Compatibility tabs from the Target window.
Note that DxWnd runs one game or app at a time.