If you mean ruler foot for using long arm rulers then there are several threads about them. The foot that fits any machine is the the Westalee ruler foot. There are threads about it and they have YouTube videos as well.
Bernina has a foot for their longarm but they are not recommending it yet for domestic machines. Take a look at Amy's site as well for lots of good info on ruler work at freemotionquiltingadventures.blogspot.com/