This tool is something I put together as I wanted to play with the Google Analytics API a little, and I was frustrated by how bad Google Analytics is for showing what browsers people are using on your site. Google Analytics doesn't allow you to see the browsers as a percentage of visits over time, and so requires lots of munging to be useful.
This tool will connect to your analytics (you'll have to authorize it with the handy screen), and will show you these figures in better way, including a breakdown by version. It isn't great, but its free. :)
For the graphs it uses the awesome free version of HighCharts.
Currently it only shows IE, Safari, Chrome and Firefox because I'm lazy and thats what I wanted. You can hit me up on twitter if you have any comments: @TomAnthonySEO.Authorize and get yummy data!