It is not souldat, is is soldat. A soldat is a Polish 2D multiplayer game for Windows and Linux. It is a side-scroller inspired by Liero and Scorched Earth, combined with elements from Counter-Strike and Worms The game is shareware. Registration unlocks extra aesthetic options, such as colored jet flames and custom interfaces. The latest version, 1.5.0, also includes a minimap and changeable screen resolution for registered users. It can also be played on Linux using Wine.
Sources: http://wiki.answers.com/Q/What_is_a_souldat&action=edit