In addition to the technical innovations that have brought a positive degree of performance, some developments were tested in free practice but were never used in the race.
This was the case with Ferrari's vertical exhaust (tested at Hockenheim), and its floor with deflectors (tested in Austin). Also worth mentioning is the double rear wing support of Mercedes (tested in Russia), as well as Renault's deflector that channeled the air towards the sidepod intakes (tested in Baku) and the side panel replacing the "aerocat" (tested in Singapore).
While they haven’t been validated yet, some concepts may be tested and trialed again in 2019, under a very different set of aerodynamic rules. But that's a story for another day...