MIUI abbreviation of MI User Interface is a stock and aftermarket firmware for smartphones and tablet computers developed by Xiaomi. The firmware is based on Google Android operating system. MIUI includes various features such as theming support.
Xiaomi has released various smartphones, all but Mi A1, Mi A2 and Mi A2 lite of which come pre-installed with a complete version of MIUI. Xiaomi devices usually get 1 android version update, but keep getting MIUI updates for 4 years. The Redmi Note 3 runs MIUI 10. This has made various apps and features not available in the aftermarket version of MIUI, but available only through rooting.
Other than supporting their in-house smartphones and tablets, Xiaomi also offers MIUI to be flashed on other smartphone brands such as Samsung, Sony, HTC, BLU, OnePlus, Nexus and Pixel.
On February 24, 2016, Xiaomi said that the MIUI ROM had over 160 million users worldwide, and was supported on over 677 handsets.
Although the MIUI is built on the Android platform, the default user interface of its earlier iterations closely resembled iOS due to the absence of the application tray with a grid of icons arrayed in the home panels. Other iOS similarities include the app icons being in a uniform shape, the dialer and in-call interface, the organization of the Settings app, and the visual appearance of toggles in the UI. This prompted some observers to cite how the devices running on MIUI could appeal to iOS users wanting to switch to the Android platform. Recently, however, MIUI is increasingly shifting towards a design aesthetic that is more similar to the stock Android. Reports indicate, for instance, that several elements in the MIUI 10 build will closely resemble what Android P has brought onto the table such as the multitasking menu and gesture controls. This change was first seen in the MIUI 9 (ver. 8.5.11) that shipped with the Xiaomi Mi Mix 2S. The MIUI firmware already looked like stock Android P.
Another key difference that distinguishes MIUI from Android is the systems support for themes. Users can download theme packs from the Mi Market, which could drastically change the user interface of the device once installed. It even allows advanced users to tweak the hard-coded firmware of their handsets.