This new utility is for displaying display (no pun intended) information when running the Mir display server on your phone/tablet or desktop. The text output is similar to that of the "xrandr" utility but is not at all related to the X Resize and Rotate extension nor does "mirout" allow configuring display outputs at all. It's only about displaying the monitor/output information.
Mirout was written by Daniel van Vugt and displays information like the display's connector, power mode, graphics cards, display sizes, and display resolutions.
Mirout was added to the Mir Dispaly Server development code-base with Bzr revision 1315.
Besides Mirout, Canonical also recently introduced Mirping as a simple utility to handle reporting round-trip times to the server. These latest Mir additions come just days after Mir got Compositor Report, another means of reporting additional Mir information.