Minelab is a free Redmine 2.5.x theme inspired by Gitlab, written in Sass. It uses Bourbon for cross browser compatibility, Neat for responsive grids and Font Awesome to replace all the stock icons. It also mimics Gitlab's page loading effect using PACE and CSS animations.
Minlab supports all the free and lite plugins from RedmineCRM. Support for more plugins is coming in later versions.
To install Minelab, you need to unzip it and copy it's contents in Redmine/public/themes. Then visit Redmine>Administration>Settings>Display and select Minelab theme.
Make it responsive!
Screenshots are available at Minlab's page
Bourbon | Neat | Font Awesome | PACE