Android, developed by Google, is known for its customization options, allowing users and manufacturers to personalize their devices. It has a vast app store, Google Play, with millions of apps for almost any purpose. Being open-source, Android also supports a range of devices across various price points, making it accessible to many.

iOS, developed by Apple, is exclusive to iPhones. It’s known for its smooth, seamless performance and high-quality phone operating systems. Apple’s strict guidelines on app quality and security make iOS devices secure and user-friendly. The App Store, Apple’s app marketplace, is highly curated to ensure that apps meet strict standards for privacy and quality.

KaiOS is a lightweight OS designed for feature phones or devices that have fewer capabilities than smartphones. This system focuses on essential functions and supports basic apps like Facebook and WhatsApp. It's popular in emerging markets where high-end smartphones aren’t as affordable or necessary for daily use.

HarmonyOS, created by Huawei, was developed to reduce dependence on other platforms like Android. Initially used on Huawei devices, HarmonyOS offers a similar experience to Android but is part of a larger ecosystem that could expand to other devices in the future.