For latest info, updates, and betas please go here:
http://wowace.com/wiki/GridLayoutPlus
About
This is a Layout plugin for Grid, so Grid is required to use this addon. It's made to be a set and forget layout manager. You just set your layout parameters and the layout will automatically change depending on what is available. The grid width (or height if you changed your layout direction) will auto-expand depending on the raid size, or max subgroup used. If you select you want to see pets, another column will be added depending on if you have hunters or warlocks in your raid. Tanks will be shown if you enable the option AND Blizz/oRA/CTRA tanks are set. etc.
More info:
http://wowace.com/wiki/GridLayoutPlus