This is a vector addition/subtraction program. You can drag the "head" and "tail" of the red and green vectors to change the size, and you can drag all three vector around by dragging their center area.
This lets you observe the "head and tail" addition method for graphical vector addition. The blue vector is the result of A + B.
Witten by Raman Phaff. Shockwave is being phased out as it is no longer supported in modern browsers.