Busan is an actor implementation that is currently under heavy development and is experimental in nature. It is not currently usable.
The project lacks any real documentation at this time other than reading through the source code. The project will have better documentation once it reaches an MVP state.
If you are interested in additional context behind the project or technical decisions, then the decision logs may be of particular interest.
The project is currently licensed under the GNU GPL v3 license because this is just a personal project that I don't intend to make any money on.