Note: there is also a FAQ available.

Installation:

Install the modulator like any other addon. (Open Blender, go to Edit > Preferences > Addons, and browse to the .zip file you just downloaded).  The other .zip file contains three libraries with more than 250 assets. You see some of the assets in the image gallery. 

Usage of the Modulator

Preparation
First, load some libraries in Modulator: N-Panel > Modulator > Assets libraries. Then, click on the + button and browse to one of the libraries. You can add multiple. 

Using
Press Ctrl+Enter to see the previews of the assets (before version 1.6, it was Shift+Enter). Next, click on the asset you want to place in the scene. (You can press Shift to select multiple). Here are a few shortcuts:

Grid snapping (default, or press 1): 

• X, Y, Z: to change the grid orientation. (Mostly, I use Z).
• Up/Down:  to move the grid up or down.
• Left/Right:  to rotate the asset on the global Z-axis
• Ctrl Left/Right: to rotate on another axis
• Insert/Delete: to adjust the size of the asset
• + or -: to change the grid size
• Ctrl: snap the asset to half the grid size

Face Snapping (Press 2): 

• X, Y, Z:  change orientation of asset
• Insert/Delete: Scale the asset with on step
• Shift: Offset of the asset. 
• Ctrl: to scale the asset
• Alt: rotate the asset

Scattering (Press 3):

• Scroll Wheel: Change Radius
• + Shift: Change Density
• X, Y, Z: Orientation of the asset
• U and S: Change scatter distribution.

One convenient shortcut I forgot is the spacebar. With the spacebar, you can select other assets (so you don't have to press Shift + Enter again).  Another shortcut I didn't mention is P: to change the pivot point of an asset.

Advanced Options

In the Properties Panel> Active tool, you can find advanced options for each mode (Grid, Surface, and Scatter) in the Properties Panel > Active tool.

For each mode there are different advanced settings. For example, for grid, you can adjust the grid's appearance (none, grid, checker).  Grid step, Rotate step, scale step, relate to the placement of the assets in grid mode. The surface mode has similar settings, and for Scatter mode, there are settings like scale, density, etc.  You have access to these settings while you are using the modal (when you are placing the assets in the scene). 

TIPS

• If you want to make your own merge-able assets (assets that you can fuse to a watertight mesh), check the Merge-able assets library on how I did it. This might inspire you.  
• In the library Scene_props, you will find profiles that you can use with the Tissue addon. Select some faces, duplicate to a new mesh, use a profile with tissue and solidify. 
• If you like corridors, take a look at the MOAS-GEN addon for generating modular assets. 
• Interesting is to use an array and curve modifier on an asset and make your own library. 

Tutorials and more documentation will follow soon.