In a previous article, we took some time to describe our own hack to provide multiple wordpress installation on a single web host, with multiple databases instead of multiple prefixes.
In this article we describe how to manage multiple wordpress install
http://infinitewp.com/ : a client/ server installation that requires a webhost for the management software and a plugin on each wordpress installation you want to manage. This plugin is free and comes with a lot of features that simplify multiple wordpress website management :
Additional plugin (50$) allows cloning / duplication of a wordpress site
https://managewp.com is a subscription based wordpress management tool