Legato composer is the MHGC designer tool for designing and building graphical user interfaces (GUIs) using Legato widgets. You can compose and customize your screens in a what-you-see-is-what-you-get (WYSIWYG) manner, and generate code associated with various LCD display dimensions and resolutions. 

If you are new to Legato composer, you can take a look at the screen shots below. Legato composer is currently in a beta version. It is functionality compatible with Aria composer and approaching feature compatibility. 

The MHGC designer for Legato is launched from the MPLAB Harmony Configurator (MHC) Tools menu as shown below: