The ShareX borderless window tool removes the standard frame from another desktop window and resizes it to the selected monitor. It is useful for applications and games that do not provide their own borderless-windowed mode.
Open it from Tools -> Borderless window.
Run the same toggle again for that window to restore its original border and window size. The target application remains running throughout the change.
You can assign Borderless window or the active-window borderless action to a ShareX hotkey for faster toggling.
The tool identifies a target by its window title. If several windows have the same title, the intended window may not be selected. Applications can also recreate their window or change its styles, which can undo the borderless state.
Some games and protected applications manage display mode internally or block external window changes. In those cases, use the application's own borderless setting when available. Save work before experimenting with applications that react badly to resizing or style changes.