Kaspersky has been toying with a free version of its widely respected antivirus solution for a while now on the company's own Dev Builds server.
Recently, the company released Kaspersky Free to the public. While not the first free product that Kaspersky has released, it is the first free full-blown antivirus solution the company has released.
The main caveat at this time is that the product has only been released official in Russia and the Ukraine.
While that is the case, downloads don't seem to be geo-restricted at this point in time. Please note though that the interface is mostly in Russian which is problematic if you don't speak the language considering that it is usually a good thing to understand what a security message means before reacting to it.
Also, you may run into activation issues if you run the program in a region that is not Russia or Ukraine. If that is the case, features are limited until those issues are resolved (for instance by using a VPN).
I expect big things from Kaspersky's free Antivirus to be honest. Can't wait for the English release. It's the second company now that releases a free version of their products (Sophos being the first).