A cloud-based supplement to your main security software
Here's something of an odd one; Immunet is a tiny cloud-based AV solution that's designed to run either independently or alongside your existing antivirus software. The former option isn't, perhaps, the best one; AV-TEST offers no indication as to its effectiveness, and Immunet's reputation – while strengthening in recent years – isn't that of an AV marvel.
Download Immunet AntiVirus
That said, as an accompaniment to a known strong solution, we can see no reason not to at least give Immunet a shot. It's all based on collective immunity, meaning the more people use it and report back with threats, the stronger its protection becomes. Like a vaccine for your PC. There was no noticeable slowdown on our test machine when running it alongside Avira, although in real terms it's going to hammer your CPU a little when scanning. It's also, if such a thing matters to you, almost comically ugly.