This version of Peggle was designed as a promotional tool for the release of Valve's The Orange Box. And is available for free on Steam or included in the Windows version of The Orange Box.
It contains the same traditional gameplay that the other Peggle games use. There are Pachinko-styled balls dropping from the top of the screen that then bounce off of pegs arranged around the board. The object is to remove all of the orange pegs. However, this version's levels are all themed on The Orange Box games (Half-Life 2, Team Fortress 2, Portal).
There are 10 levels total as well as 5 Master challenges. The Duel Mode allows the player to go up against another player or the CPU.