FastThreadAnalyzer is the tool which helps to debug you java stack traces.
It provides various insights about the stacks , club the similar stack together and provide you direction or in some cases the exact issue.
Some of the screenshots of the tools:
Threads of same thread pool grouped via thread state:
Now you see these threads group via similar stacks , which provides great insights on what type of flow are stuck:
Overall Thread State Wise Grouping:
There are various other type of grouping of stacks as well like based on length of stacks , deadlocks and so on.
If your org works on java that this should be the default tool to debug the application issues.