This is an old hobby OS project from 2009, started out of curiosity, continued out of enjoyment, and abandoned when the goals were clarified and the approach no longer suited. Those goals live on and are being accomplished in userland today by Mango.
For instructions on compiling and running in QEMU, see the old README. The API section there is empty because the notion of userspace programs just barely existed at the end of the project's life.
The most interesting thing about the kernel was the kernel's memory allocation, since the goal was good IPC. Most of the other code is probably pretty pedestrian for hobby OSes.
A lot of learning took place over the course of this project, and its last year of development is documened in the devlog (NB: This piece of writing is unmodified from the original, and is long past its expiration date. In particular, it occasionally reflects opinions about software development, software design, writing style, and many other things, with which I no longer agree.)
Toast is licensed under the MIT License