Here is some detail about Xous that includes a list of available services and applications at the bottom: github.com/betrusted-io/xous-c

FWIW: Xous is written in Rust (a plus for security) and seems to be specifically targeted to the Precursor device. However, it is a basic embedded OS and currently has no community outside of Precursor users. I think the community size and composition (programmers who understand embedded development) will make or break it.