Android 4.1 Jelly Bean (API Level 16) is the successor of Android 4.0 Ice Cream Sandwich.
Google announced Android 4.1 (Jelly Bean) at the Google I/O conference on 27 June 2012. Based on Linux kernel 3.0.31, Jelly Bean was an incremental update with the primary aim of improving the functionality and performance of the user interface. The performance improvement involved "Project Butter", which uses touch anticipation, triple buffering, extended vsync timing and a fixed frame rate of 60 fps to create a fluid and "buttery-smooth" UI. Android 4.1 Jelly Bean was released to the Android Open Source Project on 9 July 2012, and the Nexus 7 tablet, the first device to run Jelly Bean, was released on 13 July 2012.
For more information about new features visit Android 4.1 API Documentation.