One UI

One UI is a modified Android ROM made by Samsung for Samsung devices. They use the original Android Open Source Project

it was originally announced during Samsung's developer conference in 2019 alongside the Galaxy S10 series, Galaxy Buds and the Galaxy Fold and was released the same year.

One UI 1
One UI 1.0, the first version of One UI, brought about many features which were becoming increasingly popular among various apps and iOS. First and foremost, dark mode was added to make viewing in dark spaces easier on the user's eyes. This feature was included in many apps and eventually brought to iOS 13 and Android 10. The first version also brought native screenshot editing tools, refined curves, refinements to the Always-On Display (tap to show), an upgraded Bixby with support for remapping the Bixby button, and a new way to navigate the device: gestures. While Android 9 Pie did come with gesture support, it was only available on Pixel devices and stock AOSP devices and is said to be 'half baked' by many users. However, Samsung decided to create their own gesture system to navigate devices with OneUI installed. All you had to do was swipe up from the bottom of the device in the three locations of the 'buttons' to navigate. There have been many mixed reviews of this system,.

One UI 1.1, a minor update for One UI, brought a few camera, fingerprint, and facial recognition stability fixes and performance optimizations. This update isn't available on the Galaxy S8, Note8, S9, and Note9 range, but was an OTA update for the Galaxy S10 series devices. It launched with the 2019 Galaxy A series devices, such as the A30, A50 and A70.

One UI 1.5, another minor update, was primarily for Galaxy Smart Watches, however, does provide native Link to Windows support. It launched with the Galaxy Note10 series devices. It also had 3 notification sounds go through minor changes.

One UI 2
One UI 2.0, the second generation update to One UI, provides Galaxy users with a skinned Digital Wellbeing experience, a more refined UI in some default apps such as Device Care, a minor UI change to the clock position in quick settings, a native screen recorder, the new Android 10 gesture system, Dynamic Lock Screen (different wallpaper with every unlock), a Trash folder in Files, native Android Auto, and harder Location permission access. OneUI 2.0 has already rolled out to Galaxy S10, Note10, Galaxy S9, and Note9 range.

One UI 2.1, a minor update for One UI 2, brings support for Galaxy devices that support 120 Hz fresh rate, Quick Share, Music Share, additional camera modes, and native support for Live Captions. It is first launched with the Galaxy S20 series devices & Galaxy Z Flip. It also arrived for other devices such as the Galaxy S9, Note9, S10, Note10, Galaxy Fold, and select Galaxy A (2020) devices as a software update.

One UI 2.5, Samsung rolled out One UI 2.5 with the Galaxy Note 20 series, and the update is now making its way to the Galaxy S20 and older Samsung phones. One UI 2.5 doesn't bring radical changes to the UI, but there are plenty of new feature additions to the camera, DeX, gesture navigation, and other services.

One UI 3
One UI 3.0, based on Android 11, was released for Galaxy S20 devices beginning December 2, 2020. The update includes a few noteworthy revisions, such as a translucent notification panel, new volume controls positioned on the right of the device alongside the physical volume keys, slightly enhanced widgets, and smoother animations and transitions throughout the whole UI.

One UI 3.1, a minor update for One UI 3, first released with the Galaxy S21 series, has started rolling out to other supported Galaxy devices, starting with the Galaxy S20 series on February 17, 2021. There are no notable user interface changes. It contains many new camera feature improvements such as improved touch autofocus and autoexposure controller and improved Single Take feature and software implementations such as Object Eraser, Multi Mic Recording, Eye Comfort Shield, Private Share and others.

One UI 4
One UI 4.0, is a upcoming One UI release that will bring Android 12 to Samsung devices, as of July 13 2021 there have been "leaks" online speculating Features, Release Date, Supported Devices and More, but nothing has been officially confirmed by Samsung yet.

One UI Core
One UI Core is a slimed down version of One UI for budget & lower end devices, One UI Core has less preinstalled apps and features than regular One UI.

Note: One UI Core features are different from one device to the next.

Device Releases
One UI 1.0 based on Android 9 Pie was periodically released to the Galaxy S8, Note8, S9, and Note9 devices throughout January, February, March nd April 2019. Newer Galaxy A and M devices also have the new Samsung skin as does the Note FE (Fan Edition). One UI 1.1 was released alongside the Galaxy S10 series and the Galaxy Fold.

One UI 1.5 was pre-installed on the Galaxy Note10 devices after Samsung's partnership with Microsoft to bring better mobile integration to Windows 10. While the Galaxy S7 series and Note 5 devices did not officially receive the update from Samsung, many developers in the Open Source community have ported the system to these devices.

One UI 2.1 is stable for the S10, Note 10, S9, Note 9, and Tab S6 devices. It was pre-installed on the S20 and most Samsung devices released in 2020.

One UI 2.5 is pre-installed on the Galaxy Note20 devices, as well as the Galaxy Z Fold 2 and the Samsung Galaxy S20 FE.

One UI 3.0 is pre-installed on the Galaxy S20 devices.

One UI 3.1 is pre-installed on the Galaxy S21 devices.