I just recently installed InfiniteWP, an awesome app for managing multiple Wordpress sites. What's different about this one? For starters, you can manage sites from different servers and domains, something I haven't come across before.
The installation was quick and easy, and I had 4 different wp sites added within minutes - 4 sites that were on 3 servers. To add a site you need to install the InfiniteWP Client plugin. When the plugin activates it gives you an activation code that you use from your central admin area.
The InfiniteWP app is free to download and runs on your own server.