How to convert an existing Elgg install to Elgg Multisite
By İşöğüçı
https://www.marcus-povey.co.uk/2012/03/14/how-to-convert-an-existing-elgg-install-to-elgg-multisite/
Elgg multisite is a version of the popular social networking platform Elgg which lets you easily run multiple Elgg sites off a single install of the software, starting new Elgg sites at the click of a button.
Marcus Povey's article.