anaheim85: Steam itself is a form of DRM as you usually have to be logged in and online to play your games. It has an offline mode trhough which works for some and others not. But some games can also be played without starting steam by simply starting their .exe from within the file folder.
Not sure I agree it is completely drm by itself, any game that takes advantage of steam drm features are then drm but steam is just an installation platform only slightly different from gog etc outside of this. With gog you have to log in to get the installer and then you can back it up and use it, but if you need to get it again or get updates you have to log in.
In steam you have log in to get the game just the same, you just happen to get the actual game files instead of an installer, at which point the game can again be backed up and used where you want and without the.steam client. Just like gog you would have to log in to get a replacement or update. I would argue that for the drm free games steam is not a form of DRM just a different online store method than gog but it does have restrictive drm options available for publishers.