Esfos

Esfos, an acronym for Esten Phone Operating System, is a mobile operating system developed by Esten, the system was released in 2001 and ended its development in 2013. The later version was based on the Android kernel.

2004-2013
The last cell phone to use Esfos was Esten Elite 3 in 2013, which is later integrated to Esten Complex 8, ending its development.