Like other commenters have said, there is KaiOS. It's a rather neat environment actually - Firefox itself shipped with all the development tools and means to sy

Like other commenters have said, there is KaiOS. It's a rather neat environment actually - Firefox itself shipped with all the development tools and means to sync apps to the device. I wrote a simple IRC client for the Nokia 8110 4G, which has its very own hacking community (called Banana Hackers) and it was great fun. However as those devices aren't that powerful, you really don't want it spend a lot of time deal with remote content/media. That's all, felt like the right place to share this thought.