Alternate Second Life Viewers

Many people complain about Second Life’s drain on processor performance. 

Linden Labs created this wiki page with alternative Second Life viewers that might be of interest to those trying to experiment with Second Life. Some of them claim offer a cleaner, easier to navigate user interface. 

I am experimenting with some right now and will let you know (Mac users) my opinion about them. Other Mac users and also Windows users are more than welcome to post their favorites and opinions here as well.