I thought the Inter 18 was around before F18 (it had a carbon mast) and was grandfathered in in hindsight after F18 came about. - I don't think that counts.
Pete Melvin and Gino Morelli designed the Inter 18 specifically for the Formula 18 Class Rules and was sold with the aluminum mast in Europe. The carbon mast was an "extra cost" option sold exclusively (I think) in North America. Nacra also offered a larger mainsail for the carbon mast Inter 18 in the 2nd or 3rd year. All of the Inter 18s can be fully legal F18s if you use the aluminum rig and F18 sails.
