Normally UT2004 only allows you to dodge or walldodge once during a jump and also add one double-jump somewhere in the whole move. Also at the end of a jump you have to wait a bit before you can dodge again.
Multi Dodging changes these rules so you can:
walldodge whenever you are near a wall even if you already (wall)dodged
always add a double-jump after a dodge or walldodge
dodge right after landing without any delay
optionally enable boost-dodging
Additionally Multi Dodging can gather movement stats like speed, distances and air time of a jump to display them on the HUD.