In a curious move, Valve have made some of their titles available through a rival digital distribution platform, Impulse. Impulse was acquired in 2011 by GameStop, which is another curious move. When your main source of income is from selling games, it would make sense to have some of PC's biggest games available on your platform.

Valve's games are now available through Impulse, which include Left 4 Dead and its sequel, Portal 2, The Half-Life Complete Collection and The Orange Box. Strangely, all games require Steam activation, which means you'd have to be using Steam at the end of the day. This hasn't affected Impulse, where they've said in a blog post:

Some of the greatest, most creative games of the past decade (and the one before that) are now available! Legendary developer/publisher Valve is now available! Whether you enjoy hitting things with crowbars, the power of gravity, making holes in walls or making large holes in the undead, Valve's games will suck you in and won't let you go! There's more quality gameplay here than you can shake a crowbar at!

I do like the last bit, "there's more quality gameplay here than you can shake a crowbar at!" Nice skills there, Impulse.