It is called Cor-A-Vent: http://www.cor-a-vent.com/
Here's a drawing that shows one application of the product on a home with no soffits or overhang: http://www.cor-a-vent.com/s400.htm
I have precisely the same problem that you have -- no soffits and no overhang. However, I may not be able to use the product because I have a brick ridge that sticks out from the wall just below the fascia and it would block the bottom of the Cor-A-Vent. Also, the Cor-A-Vent may push the fascia and gutter out by an inch and you need to have adequate roof/shingle overhang so that water from the roof falls into the gutter rather than behind it!
You could always create an overhang by installing rafter tails, sheathing and a course of shingles...
Be certain to keep the airspace clear from the end of the rafters into the attic. You can buy a shaped foam spacer that fits between the rafters to insure good airflow and prevent blockage by the insulation.