The Series 90 (formerly Hildon) is a platform for mobile phones that use Symbian OS. It was developed by Nokia in collaboration with Psion. It was released in 2003 and was going to be the platform for the Nokia 7700 which was cancelled, but did eventually make it to market with the Nokia 7710.
Nokia discontinued Series 90 as a platform, but merged its technology into S60.[1][2] Although only one production Series 90 device was made, a form of the GUI continued on as Nokia's Hildon user interface in the Maemo shipped with Nokia Internet Tablets.