Yup. Used one years ago, like this:
http://www.abilityhub.com/mouse/foot.htm
A couple of different configurations depending on which one you buy. The one I linked to is movement controlled by the left foot (like a track-point on IBM laptops) and the right foot to click.
Other types include left foot for vertical movement, right for horizontal movement. Each foot can click as appropriate.
They take a little getting used to, but it's supposedly more efficient than having to move your hand to the mouse & back to the keyboard. Also supposedly prevents RSI's, whilst encouraging back posture.