These are separate packages of shaders and scripts that reference Alloy and build on top of it. Here are a few official examples:
Deprecated Alloy scripts and shaders. They won't receive new features, and may be dropped if they interfere with newer shaders. These exist to facilitate migration or to support projects that are nearly ready to ship. Please refrain from making new content with them.
Betas, experiments, and one-off shaders that we've done for personal/commercial work. They're NOT officially supported or documented, but may be added to the official set if there is sufficient demand.