which is the solid modeling kernel based on csg

hi all!!

which is the solid modeling kernel which uses csg algorithms??

both parasoid and acis are based on b-rep...
is there any such modeler availabe which is based on csg???

if not ( that is my sure speculation) then can we say that csg
representation is obsolute..
i posted one earlier message regarding csg and brep and someone told
me that in autocad we can build the object using csg
operations(union,add,and subract etc..).but autocad is based on acis
kernel which uses brep representation..
now i am more confused..
so how will one differentiate between building a model using csg
techniques and storing them in brep...

regds,
yogesh joshi