Imagine not having the hassle of Windows, but still being able to run (most) Windows programs? That's the goal with ReactOS, which builds on the old Windows NT architecture as an open source operating system. And it only takes a 150MB to install it, so it's small. You can grab it as a full installer, or make a LiveCD version that boots off a disc to give it a try.
Something to always watch for: crapware installers. To make ends meet, many creators of otherwise great free software, or the services that offer the programs for download, bundle in things you don't want. Worse, the installation routine obfuscates the steps, so you provide the unwanted program tacit permission to be installed. For more about how to spot and avoid this problem, see How to Clean Crapware From a New PC, and check out the Uninstaller section of this very free software collection.
Freeflys: Another strong contender in the freebies space, Freeflys has appeared on NBC’s Today Show, The Doctors, Fox News and a handful of other media outlets. Similar to most of these sites, Freeflys utilizes email alerts to tell users about free-sample offers as they happen. The site also allows you to search for a specific product with the handy search bar.