Kefitzat Haderech - Incunabulum of the Uncanny Gates and Portals is a generic RPG supplement about portals and dimensional gates. The topics covered are why are portals cool?, what should I do with them? and how do I build them?
It also comes with a muleload of tables to generate portals and everything related, including PORTATRON, the one-stop-system of portal generation
KHIotUGaP (not an official acronym) also contains The Infamous d666 Quick Portal Destination Table, which does what it says on the tin. Because we wanted to have a d1000 table and have the longest OSR table as some kind of joke, but then we realized that 216 portal destinations ought to be enough for everybody.