That is not a typo, Valve is giving away copies of Portal for the low, low cost of zero US Dollars and zero cents (for our Canadian users, I've taken the liberty of doing the conversion maths already and it's zero Canadian Dollars). If you don't already own Portal for some reason, get it, and quick;
this offer's only good until May 24th.
http://store.steampowered.com/freeportal/
GHOST EDIT: I would also like to point out, for those who don't know, that Steam is available on the Mac now too, with a
number of games. This offer for free Portal is good on the Mac platform as well, and any games you purchased on the PC client you will be able to download and play on a Mac without having to pay again.