GGU-CAD: "Trim" menu item
This menu item allows two lines to be joined at their intersection by clicking the lines, one after the other.

The shorter of the lines is extended to the intersection. The shorter end of longer lines is deleted as far as the intersection. If, as in the above example, the lower section of the longer line is to be retained, the upper end must first be shortened via [F7] or the lower end extended.