• Air France
• British Airways
• Braniff International Airways operated Concordes between Dulles International Airport and Dallas Fort Worth International Airport, utilizing its own flight and cabin crew, under its own insurance and operator's license. Stickers containing a US registration were placed over the French and British registrations of the aircraft during each rotation, and a placard was temporarily placed behind the cockpit to signify the operator and operator's license in command.^([266])
• Singapore Airlines had its livery placed on the left side of Concorde G-BOAD, and held a joint marketing agreement which saw Singapore insignias on the cabin fittings, as well as the airline's "Singapore Girl" stewardesses jointly sharing cabin duty with British Airways flight attendants. All flight crew, operations, and insurances remained solely under British Airways however, and at no point did Singapore Airlines operate Concorde services under its own operator's certification, nor wet-lease an aircraft. This arrangement initially only lasted for three flights, conducted between 9–13 December 1977; it later resumed on 24 January 1979, and operated until 1 November 1980. The Singapore livery was used on G-BOAD from 1977 to 1980.^([267])

https://en.wikipedia.org/wiki/Concorde#cite_note-272

Was really only Air France and BA, but these two had a bit of a crack too.