Product Mapping and Discovery Trees
Product Mapping and Discovery Trees were tools that were discovered when FAST emerged. They helped visualize work, track it, and create a shared context and understanding. The discovery trees really helped with Fluid Teaming as an incoming team member could very quickly get a picture of the work and the context it sat in.
While these tools are described as being part of FAST in the 2.12 version of the FAST Guide and earlier, from version 3, they will be useful additions or framework aspects of FaST and not a part of the core.
Some Blogs on Discovery Trees
Working With Discovery Trees by Steve Kuo