In other words, yes, avast Free edition IS free, and always will be (as far as we know). The only limitation is that you have to re-register yearly, which consists of clicking a register link and providing your name and email address.
The 30 day trials come with all versions. Free requires you to register by the end of the 30 days, while the others require you to pay for a license at the end of 30 days.
Hope that clears that up.