Windows only: Freeware, lightweight anti-spyware application ThreatFire monitors your computer for malware and blocks new threats in real time. There are a lot of freeware anti-spyware apps out there, but the difference between most of them and ThreatFire is the always-on, real-time protection—as opposed to on-demand scanning. The catch is, ThreatFire does not do on-demand scans in the free version. All that really means is that you can download one of the many other freeware options (like AVG Free and Ad-Aware, for example) for on-demand scans and run ThreatFire to cover any immediate threats in real-time. ThreatFire is freeware, Windows only. Everybody's got their favorite anti-virus and anti-malware apps, so let's hear yours in the comments.