State tells you the current key stroke that has been typed by the user
Elements gives you the complete list of elements that is referenced by the current rule, breaking down stores, indexes, any and other statements into their component characters.
The call stack shows you the sequence of rules and groups in the keyboard file to reach the current rule.
The deadkeys tab lists the currently recorded deadkeys in the context, and highlights them when you select them.
The regression testing tab allows you to automatically test various parts of your keyboard when you make changes to it, making sure that changes you make do not affect the basic functionality of the keyboard.