BiCR, or binary container runtime, is a custom container abstraction built on top of Podman that supports creating containers from a single binary over gRPC. There is a base filesystem that all containers are based on that is stored on a Btrfs partition for copy-on-write support.
It was initially designed for Servlio, but was never actually used since it would have required too much extra overhead for not enough tangible benefit over existing solutions. Despite this, it still served as a good learning oppertunity, and I now believe that I have a much better understanding of how containers work under the hood.
This project started off as a completely custom container runtime operating right next to the OS, but eventually transition up the abstraction layers. The first transition was to runC which is the basis for many of the popular container tools as it made managing and sandboxing processes far easier. However, networking and logging soon became a problem, which led me to switch to Podman as the final abstraction, since it supports all the necessary features with an easy to use API.