UK journalist and Edge columnist Steven Poole has released his book Trigger Happy as a free PDF download, under Creative Commons. I'm not 100% sure why Poole's done this, but I think it's to help promote Unspeak, his latest work.
So, what's Trigger Happy then? Steven Poole is glad you asked:
Trigger Happy is a book about the aesthetics of videogames - what they share with cinema, the history of painting, or literature; and what makes them different, in terms of form, psychology and semiotics. It was first published in 2000.
Poole mentions on his blog that the offer is for a limited time only, although he's unsure exactly how long "limited" is.
Trigger Happier [stevenpoole.net, thanks Bjorn]