PDFCreator
PDFCreator is an application for converting documents into Portable Document Format (PDF) format on Microsoft Windows operating system. Once installed, it allows the user to select PDFCreator as their printer, allowing almost any application to print to PDF.
It is GPL-licensed free software, written in (and can only be compiled in) Microsoft Visual Basic, and depends on a few proprietary Windows components, like HTML Help and Windows Printer Drivers, which practically makes it only available for Microsoft Windows environments. The actual PDF generation is handled by Ghostscript.
Besides being installed as a printer driver, PDFCreator can be associated with .ps files to manually convert PostScript to PDF format.