Android 4.1 Jellybean OS is summarized as follows:
1) It introduced Project Butter to address screen lag and smooth out touch response, animations, and performance.
2) Notifications were improved with a stacked display that is easily navigated by pinching and swiping.
3) Voice recognition was enhanced to allow offline use and download of accent models. It is also better integrated with Google Now.
4) Overall, Jellybean focused on refining the user experience through improved graphics, notifications, voice features and other minor updates rather than major new additions.