Rashi's commentary on the Gemara is incomplete on some tractates. The commentary of his grandson, the Rashbam, is printed in its place in Bava Batra and Pesachim.
Did the Rashbam only write a commentary on those parts of Shas that Rashi had not completed? Or did he write on more tractates, but only those that Rashi hadn't written on were printed? If so, is the rest of his commentary still extant?
Wikepedia doesn't know about it, but that doesn't count as a source.