Lomography is the commercial trademark of Lomographische AG, Austria for products and services catering to the Global Modern art community of Lomographic photography.But this doesn't really tell us anything, not anything relevant to creating these interesting photographs anyway.
What I've learned by searching the web for terms like "lomography", "lomo", and "holga" (the last two seeming to be a sort of slang) is that this is a style of photography. Lomography.com appears to be the official home of Lomo on the web so I highly recommend checking there for more info. But back to what I've gathered so far...
There are ways to create these effects digitally, but I don't think they are as beautiful and they certainly don't lend themselves to the miracle of spontaneity that seems to be what the fun of taking lomo photos is all about. If you'd like to attempt a digital lomo effect I would recommend playing around with the levels of contrast and saturation then adding a vignette.
Because I love the look of these photos so much, I'm considering getting a few of these cameras and maybe even setting up a dark room in my basement. I'll keep you posted.