I came across this post from The @ Company a while ago, and I have to admit that while I haven't done a deep dive on this technology yet, it has me intrigued. It especially seems suited for apps aiming to provide end-to-end data encryption between users.
In a nutshell, the tech is described as follows (quoting directly from the atsign.dev website):
The @platform is designed to help developers create end-to-end encrypted mobile applications. A full stack platform written in Dart and Flutter, it includes a wide range of libraries, services and widgets specifically designed for creating privacy-first applications on any platform.
For those wanting a quick demo of the tech, you may find this recent demo day video helpful.