All through December you can win a copy of an avast licence. Each day at midnight (UK time) a new question is asked. Just choose an answer and put your email address and click send, it really is that simple.
Nothing is ever really truly "free," there's always something. That's usually the course when signing up commercial version giveaways, usually in the form of getting email offers/adverts which can easily be opted out of or blocked. That and if you install it they can garner info anyway such as IP address, etc., and possibly other info if having to submit detected items.