Mercenary Kings is a side-scrolling shoot 'em up game developed and published by Tribute Games. The game, created by the team behind Scott Pilgrim vs. the World: The Game, was funded by Kickstarter and will be released for Windows and PlayStation 4 in Q3/Q4 2013. An early-access version of the game was released on Steam on July 23, 2013.
Mercenary Kings is a side-scrolling shoot 'em up similar to games such as Metal Slug, in which players fight against hordes of enemies and rescue hostages. Players have the ability to craft their arsenal and upgrade their armor, as well play alongside three other players, locally or online.
Source: Wikipedia, "Mercenary Kings", available under the CC-BY-SA License.