Evolve is a new, simplistic, minimal, light GTK3 theme. It is easy on the eyes and comes with a matching theme for GTK2 apps. The theme is compatible with the latest GTK 3.2. Evolve uses the Adwaita engine for the GTK3 theme and Murrine for the GTK2 theme.
To be frank, though GTK3 theming is a lot easier than GTK2, the biggest challenge is making a matching GTK2 theme. I don't understand GTK2 theming and it is much of work for me to learn it. But then, people won't use your theme, no matter how beautiful it is. Because lots of apps are still in GTK2 and they will look out of place.
Thanks to Andrew for writing about it in his famous blog here, as well as hosting it in the WebUpd8 themes PPA, making it easy for Ubuntu users to install. These are the things that encourage me to create more themes and dedicate more time. Especially Andrew has helped me a lot and he is the best blogger I met ever :)
As, Evolve is available in the WebUpd8 themes PPA, Ubuntu 11.10 users can install it using the commands below,
sudo add-apt-repository ppa:webupd8team/themes
sudo apt-get update && sudo apt-get install evolve-gtk-theme
sudo apt-get update && sudo apt-get install evolve-gtk-theme
And just for Ubuntu users, the theme also supports Unity :) The Unity panel is also themed and gets its own Window controls.
If you use any other distro, you can download it here, complete with installation instructions.