This wasn't always the case because of fragmentation due to different device screen sizes and differences in levels of Java ME support on various devices.
As a pioneer that established the smartphone industry, it was the most popular smartphone OS on a worldwide average until the end of 2010 – at a time when smartphones were in limited use, when it was overtaken by Android, as Google and its partners achieved wide adoption.
Symbian OS was essentially a shell system and required an additional user interface (as middleware) to form a complete operating system.
Symbian OS became prominent from the S60 (formerly Series 60) platform built by Nokia, first released in 2002 and powering most Nokia smartphones.
Applications of these interfaces were not compatible with each other, despite each being built atop Symbian OS.
Nokia became the majority shareholder in Symbian Ltd. The non-profit Symbian Foundation was then created to make a royalty-free successor to Symbian OS – seeking to unify the platform, S60 became the Foundation's favoured UI and UIQ stopped development but MOAP continued in the Japanese market.