Contains shaders in flux and in development that may change completely tomorrow. Use these with caution, and its probably safest to use them in unlinked mode, because if you download a new version in the future, the behavior may have changed enough such that your old scenes no longer work.
These are shaders that are mature enough and stable enough that the intent is that the shaders interface and behaviour won't substantially change in the future. It may gain parameters, but defaults should be compatible with the previous version. These shaders are candidates to be included in the shipping set in the next version.
These are shaders submitted by users.
If you want to contribute, read the how to submit documentation for details.