S60 (formerly known as Series 60) is one of the major smartphone user interfaces. It is developed mainly by Nokia and uses the Symbian OS as its base. Besides using it in all of its own smartphones, Nokia also licenses S60 to other manufacturers such as Samsung and LG.
S60 is capable of running native third-party S60 applications as well as regular Java applications.
There are several releases of the S60 UI and chronologically they include Series 60 (2001), Series 60 Second Edition (2004), Series 60 3rd Edition (2005) and S60 5th edition (2008).
Thrid-party software written for S60 1st Edition (S60v1) or 2nd Edition (S60v2) is not compatible with S60 3rd Edition (S60v3) and later because it uses a new version of the Symbian OS (v9.1).
The latest S60 5th edition was announced in October 2008. Nokia decided to move directly from the 3rd Edition to the 5th Edition "as a polite gesture to Asian customers" since the number four is considered bad luck in some Asian cultures.
The major feature of S60 5th Edition is support for high-resolution 640x360 touchscreens. Before the 5th Edition, all S60 devices had a button-based user interface.
S60 5th edition has some support for third-party software developed for S60 3rd edition but, it's currently limited and somewhat hit-and-miss.