A Rust kernel running on bare UEFI (no separate bootloader). Very early stage.
Check the wiki for some notes about this thing.
Basically, the eventual goal is to build a non-opinionated microkernel that can load regular ELF64 programs as kernel "modules". Actually, just fairly conventional processes, except running in kernel space (they are assumed to be written in Rust and reproducible, so that hardware protections are unnecessary, similar but unrelated to Microsoft's Singularity project).
The core micro/nano/whateverkernel will link up the loaded applications with a builtin dynamically linked library that exposes its functionality, moving the responsibility for higher-level problems (such as syscalls) into these loadable binaries, and also allowing simple emulation without virtualization for debugging purposes.