The TreeTableView control is a new control targeted at JavaFX 8.0. The Jira issue for this feature request is at RT-17288, but this wiki page should cover the main points in summary.
TreeTableView API Discussion
Discussion of the currently-in-development TreeTableView API, including open questions that need to be discussed further.
TreeTableView API Examples
A number of worked examples demonstrating how to use the TreeTableView API in its current form.
TreeTableView User Experience Documentation
Documentation written by the UX team inside Oracle that outlines the required functionality and user interactions of the TreeTableView control.
TreeTableView Implementation Details
A brief overview of the implementation details behind the TreeTableView control.