RelationsInspector

This tool displays graphs of data relations, like a filtered asset view or scene hierarchy... or the communication between PlayMaker state machines... or links between Dialogue System conversations. It ships with a number of add-ons and lets you easily write one for your own use case.
Manual | Discussion | Twitter
Included add-ons
* scene hierarchy
* project view
* asset references
* object dependencies
* uGUI event overview
* PlayMaker FSM communication
* Master Audio events
* Dialogue System conversations
* Core GameKit killable prefabs
* Inventory Pro item references
* S-Quest quest editor
* Inventory Master crafting
Write your own add-on! It can be as simple as putting two attributes on your data types, or as involved as writing your own graph editing rules and constraints, node widget GUI and context menu items.
Features
* your tools can control it through API
* open source
* works with Unity 5
* works with Unity free and pro
* light and dark skin
* automatic layout
* layout saving
* history navigation