You can find the GGro beta on Gumroad: https://giogargiulo.gumroad.com/l/ggro

It’s free to use for non-commercial projects, and there will be a commercial version available as well once it’s out of beta.

Installation:

• In the download files you'll find a zip archive containing the OTLs and a JSON file.
• Unzip the archive in your preferred location
• Copy the JSON file in the "packages" subfolder inside your Houdini home directory (typically located at Documents/houdinixx.x)
• Open the JSON file you've just copied, and replace the path with the location you've used to unzip

Notes:

• Since this is a beta, the UI and the nodes may change, so future updates may not be fully compatible with setups built with the current version. While I am going to try to avoid this as much as possible, the toolkit is still evolving so it's not guaranteed.
• Full compatibility is only guaranteed with Houdini 21. However, since most nodes are just VEX wrangles, 99% of it should work in other versions.