Series 40

Series 40, also known as S40, is a user interface used on Nokia feature phones from 1999 to 2014. It runs on top of Nokia's proprietary OS. Series 40 doesn't have its own application format, but it supports J2ME, and Flash Lite on newer versions.

There were also some Qualcomm based Nokia CDMA phones running Series 40 on top of REX OS, for example the Nokia 3806.

2nd Edition
S40 2nd Edition was released in 2003. It brought these improvements:
 * Theme support using NTH files
 * Support for more screen resolutions - 128 × 160 and 208 × 208. The latter was short lived and dropped in 3rd Edition.
 * Middle selection button support

3rd Edition
The 3rd Edition of S40 was introduced in 2005 with a UI redesign, adding some major improvements:
 * Support for 240 × 320 devices, but dropped 128 × 128 support
 * Allows running Java apps sent via Bluetooth or Infrared
 * Improved themes

5th Edition
As usual, Nokia skipped the number 4 due to tetraphobia in Asian markets. 5th Edition introduced the concept of the Lite versions, which were intended for lower end devices.

6th Edition
The 6th edition brought these new features:
 * New WebKit based browser
 * Support for 320 × 480 resolution, only ever used on the 6260 slide
 * Flash Lite 3 and MIDP 2.1
 * Simplified status bar

S40 Developer Platform
S40 Developer Platform is the name of S40 versions newer than 6th Edition, used on the Asha series, as well as later C and X series models.