Android One is a standard created by Google for Android systems, mainly targeted at people buying their first smartphone, and customers in the developing world. Android One smartphones
will run software close to stock Android, without the often extensive
vendor-specific modifications that many smartphone vendors apply.
Security updates will be handled by Google, avoiding problems some
earlier phones have had with lacking security updates. Google also makes a reference hardware design available for Android One, meaning that OEMs just have to manufacture the phone. The first set of Android One devices features MediaTek's quad-core MT6582 Mobile System-on-Chip (Mobile SoC) Source:Wikipedia
The first smartphone to be part of the Android One comes from Micromax,
one of the most popular smartphone brands in India. Its Android One
smartphone packs features that are most important for users there. Those
are FM Radio, Dual SIM support, microSD card and a low price.
The Android One program guarantees that the phones that come out of it
will run on the most recent Android release, as Google will push updates
to those phones similar to the way it handles GPE devices.
Android One smartphones were by the Indian brands Micromax, Spice and Karbonn in September 2014, and other like Alcatel, Lava etc are going to follow gradually be getting hands on it.