McDonald's just launched mobile ordering in my area (Irvine, CA). I noticed under the promotions tab there was an offer for 2 Free Egg McMuffins. I was not able to order it by itself, but when I added a drink it went through and I was only charged for the drink. I have done this twice now, so I'm not sure what the maximum redemptions is.
This is going to be highly YMMV, as only a couple of stores had this offer (I was driving by a different store yesterday and the offer was not available).
Might be worth checking the app.