You can use a wide variety of apps on KaiOS-powered phones, ranging from instant messaging and entertainment, to utilities and self-improving content. You can check them all out and download them on the KaiStore: https://www.kaiostech.com/store/ .
Note: JioPhones come with the JioStore instead of the KaiStore. JioStore has its own marketplace for apps with a different selection. For more details, please visit: https://support.kaiostech.com/en/support/solutions/articles/35000141300-why-don-t-i-have-the-kaistore-in-my-jiophone-