I played with it for a while. Apps are basically web pages with JavaScript and stuff, there’s a lot of resources at Bananahackers.net

I looked into it, but more for development purposes than installing it onto anything.

Seems like it would be easy to develop for, but the ecosystem seems to be pretty locked down due to the permissions model. There's some ability to jailbreak devices, but it's not a huge list of supported models.

For basic apps it'd be fine. But if I wanted to make custom applications for SMS, use bluetooth, make a new default dialer (e.g. to add SIP dialing), etc, it wouldn't be possible since only OEMs can "bless" those. Even the next permission level down (Privileged) requires the apps to be signed by an authorized KaiStore.

Since my goal at the time was to make a lightweight Meshtastic client, I just gave up since I wouldn't have the necessary permissions to make it work.