Does Steam periodically give you free games? I keep seeing games appear in my library with a "1 day left" or "twenty hours left" etc. message next to it, but I don't want to install something if they're going to charge me later. So...what's going on? I've noticed this almost every weekend I start up steam.

It's free for a limited time; they let you install and play it, but after it expires, you have to buy it if you want to keep playing. I believe they're called "Free weekend games."

Oooh Okay. That makes more sense than just randomly throwing free games around.

They gave Portal out for free, but that was as a promotion for the Mac version.

I got portal for free at some point too, but I seem to remember that promotion running differently.

I didn't get portal for free In any case, they usually have a discount during the free period for like 50% off or something.

Portal was unique in that there was a promo for it on Steam's site. We had a topic about that here: http://www.staredit.net/topic/11037/

If they're actually giving away a free game, we tend to make a commotion about it. Even when it's not a temporary promotion (see http://www.staredit.net/topic/13987/).