In 1975, the Space Race: Apollo–Soyuz Test Project featured the dual launch of an Apollo spacecraft and a Soyuz spacecraft.
It was both the last launch of an Apollo spacecraft and the Saturn family of rockets. The Apollo-Soyuz Test Project was the first joint Soviet-US human-crewed flight. The main objection of the Project was to test compatible rendezvous and docking systems that were being developed for future United States and Soviet manned spacecraft and stations.
Learn more at http://history.msfc.nasa.gov/milestones/chpt10.pdf