There are so many ... some for helping define the problem, some for understanding the process/system being analyzed, some for analyzing data, etc.
I would say that perhaps the most powerful ones overall are a flowchart and a logic tree.
The flowchart helps understand the system works in sequence. Some people use them but only at a high level, but they can be done repeatedly at each level to get a deeper understanding of causes.
The logic tree is a replacement for the cause & effect diagram. It allows looking at cause & effect relationships in chunks, so you don't have to be thinking about so many simultaneously. And if you can show that one of the branches on the tree did not create the problem, then all the detailed causes below it go away.
One of the things I always like to stress is that the tools are not the end in themselves, they are simply cognitive aids. They help our minds process information more effectively, both individually and as a group. So not everyone has to be a tools expert, as long as there is someone (often called a facilitator) who can help the group use the right tools in the right way at the right time.
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