The project is called “Tactility” and its website is https://tactility.one/
You can run ELF binary apps directly from an SD card without restarting or flashing the ROM. There’s an SDK for building these apps, but I haven’t made an official release yet.
I wrote a blog post with some background information: https://bytewelder.com/posts/2025/01/06/tactility-one-year-later.html
Source code and project files: https://github.com/ByteWelder/Tactility
In its current state, it’s mainly a tool for developers to be able to build prototypes or experiments quickly. From a user perspective, there isn’t enough yet. We’ll need more apps before it’s useful for end-users. I want to improve the core functionality before I build more apps: I already have to maintain about 2 dozen apps and I’d rather spend my time on building a better platform for now.