The best free open source software for Windows
FileZilla is one of those essential Internet tools that you just can’t live without. A full-featured Windows FTP client, FileZilla makes interacting with FTP sites an efficient, productive process.
OpenOffice.org is one of the tools most closely associated with the free open source movement. Encompassing word processing, spreadsheet, presentation graphics, drawing, and database functions.
Like OpenOffice.org, Firefox is another tool that's almost synonymous with free open source. It’s also the movement’s greatest success story, with more than 30 percent of Web surfers running some version of the Firefox browser.
Paint.net has a checkered past as a free open source solution. Originally released as a completely open source project, its developers were forced to scale back to a more restrictive Creative Commons License (still freely available, but without source code) after unscrupulous parties decided to rename the original and try to resell it for profit.
Media Player Classic is a tool that always causes me to do a double-take.
TrueCrypt ( RIP 2014 ) is one of those free open source utilities that fly under the radar of most Windows users. See alternatives.
PDFCreator installs as a virtual printer driver under Windows, allowing you to dynamically generate PDF output from virtually any Windows application.
7-Zip is another great example of a free open source project that takes over where many commercial solutions stop. Incorporating a wide range of decompression formats (from ARJ to ZIP, and virtually everything in between) and its own advanced LZMA-based compression engine, 7-Zip delivers performance on par with proprietary formats like RAR and ACE while remaining entirely open and extensible.
ClamWin is a free open source anti-virus solution that provides a (mostly) comprehensive shield against the majority of common malware threats. I say "mostly" because the product lacks real-time execution monitoring, a critical component of any modern anti-virus solution.