Random Rotate XYZ is an add-on, as the name suggests, allows you to rotate randomly in all 3 axis.
Alt+Q is the hotkey
It have 2 modes - Increment Random Rotation & Normal Random Rotation
Increment will let you rotate in random increments of the specified axis.
For the Normal Random Rotation, you can specify a minimum and maximum value for each axis.
You can choose between Global, Local and Custom Orientation, for the rotation axis.
What is the Custom Orientation?
It allows you to choose a custom object to determine the initial orientation/rotation of all the selected objects.
Download the simple Random Rotate Z
Random Rotate Z is a simple Blender addon to rotate multiple objects randomly, on the local Z axis.
Alt+Q is the hotkey
You can set minimum and maximum angle for random rotation, use the N panel to find those inputs.
WARNING : Use one of these add-ons at a time! Installing both will cause conflicting hotkeys