KaiOS is a mobile operating system, based on Linux, for keypad feature phones. It is developed by KaiOS Technologies (Hong Kong) Limited; a company based in Hong Kong, with largest shareholder being Chinese multinational electronics conglomerate TCL Corporation. KaiOS is  forked from B2G OS (Boot to Gecko OS), an open source community-driven fork of Firefox OS, which was discontinued by Mozilla in 2016.  
The primary features of KaiOS bring support for
4G LTE E, VoLTE, GPS, and Wi-Fi; with HTML5-based apps and longer battery life to non-touchscreen devices with optimised user interface, less memory and energy consumption.  It also features  over-the-air updates (OTA updates). A dedicated app marketplace (KaiStore) enables users to download mobile applications, or 'apps'. Some services are preloaded as HTML5 applications, including  Facebook and YouTube. As of 1 April 2020 , there are 500+ apps in KaiStore. The  mobile operating system is comparatively lightweight on hardware resource usage, and is able to run on devices with just 256 megabytes (MB) of memory.
The operating system first appeared in 2017
Hong Kong-based company headed by CEO Sebastien Codeville, with offices in other countries. In June 2018,  Google invested US$22 million in the operating system. India-based telecom operator  Reliance Jio also invested $7 million for a 16% stake in the company. In May 2019, KaiOS raised an additional US$50 million from  Cathay Innovation, and previous investors Google and TCL Holdings.
, and is developed by KaiOS Technologies Inc., a
In market share study results announced in May 2018, KaiOS beat Apple's
iOS for second place in India, while Android dominates with 71%, albeit down by 9%. KaiOS growth is being largely attributed to the popularity of the competitively-priced  Jio phone. In Q1 2018, 23 million KaiOS devices were released. 
In March 2020,
Devices that are installed with KaiOS are:
Alcatel Go Flip (known as Cingular Flip 2 on  AT&T, Alcatel MyFlip on  TracFone Wireless ) and 3088X 
Advan Hape Online ( Indonesia) in partnership with Indosat Ooredoo.
Reliance Jio's JioPhone, F10Q, F101K, F120B, F220B, F211S, F221S, F250Y, F271I, F30C, F41T, F50Y, F61F, F81E, F90M, LF-2401, LF-2402, LF-2403, LF-2403N, all branded as LYF,     JioPhone 2, F300B, F310B, JioPhone lite, F320B
HMD Global's Nokia 8110 4G, 2720 Flip, 800 Tough, 6300 4G, 8000 4G   
Energizer Energy E220, E220S, E241, E241S and Hardcase H241, H242, H280S
Doro 7010, 7030, 7050, 7060  Cat B35
 Maxcom MK241, MK281
 WizPhone WP006, launched in
Indonesia in partnership with Google and Alfamart. 
MTN 3G phone (MTN Smart S 3G) 
Positivo P70S (Brazil) 
Multilaser ZAPP (Brazil) 
Tecno T901 
Jazz Digit 4G (Pakistan)
Orange Sanza 2, Sanza XL Kitochi 4G Smart
Vodacom Smart Kitochi (Vida), Vodacom Smart Kitochi (Azumi)
QMobile 4G Plus (Pakistan)
GeoPhone T15 (Bangladesh)
GeoPhone T19 (Bangladesh)
GeoPhone T19i (Bangladesh)
Sigma mobile X-Style S3500 sKai (Ukraine)
As of February 2018
Mozilla, Airfind, Avenir Telecom(Energizer), Facebook, Google, Bullitt, Doro, HMD Global, Micromax, NXP, Spreadtrum, Qualcomm, Jio, Sprint, AT&T, T-Mobile, and Orange S.A.  
, KaiOS Technologies has partnered with
In March 2020, KaiOS Technologies partnered with Mozilla to bring the modern version of
Gecko browser engine to future KaiOS builds. 
First KaiOS smart feature flip phone
Major core upgrade to Gecko 48
 Services and 3rd party apps
Nokia 8110 4G
 KaiStore, KaiAccount, and advanced features, WhatsApp
Minor system updates
KaiAds and SIMbased cust.
Nokia 2720 Flip, Nokia 800 Tough
Major service upgrades, location service enhancement
Minor system updates, notification enhancement
Device Financing Program, Dual SIM LTE support
LF 1.6 integration, North America requirement
Nokia 6300 4G, Nokia 8000 4G
Major platform Upgrade, Gecko upgrade
With the release of the
Nokia 8110 4G, an active community around both KaiOS and the phone arose and released the first version of a jailbreak. This gave users the ability to use old Firefox OS apps on KaiOS devices, as well as flashing their devices with community-created ROMs, such as GerdaOS. 
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