Aperture Tag: The Paint Gun Testing Initiative

Aperture Tag: The Paint Gun Testing Initiative is a 2014 first-person puzzle-platform video game developed by the Aperture Tag Team. Originally made as a modification of the Valve Corporation's Portal series, it was officially approved for sale by Valve and released on the software distribution platform Steam on July 15, 2014. The game lacks the iconic portal gun of the series and instead utilizes a newly created paint gun that fires two kinds of gel with different properties. The game features new characters and voice acting, along with twenty-seven levels and a co-op mode that also includes a level editor.[1]