These tools leverage the amazing IKVM project to parse the Java class files into C# classes.
You can download the exe from Util - O2 Java Tools - IKVM Based v1.0.exe (its 20Mb since it includes the latest version of IKVM)
When you start this exe, you will see this menu:
Which is a launcher for the following 4 tools (included as *.h2 scripts which will be compiled on first run):
Util - Java Methods CallTo and IsCalledBy Mappings.h2
Util - View Java Mappings.h2
Util - Jar or Class Browser.h2
Util - View Jar File Entries.h2
And as with most O2 tools, what is really powerful is the fact that these APIs and GUIs are all easily scripted using the provided REPL C# Script environment (via REPL menu):