PDF24 offers a comprehensive set of free PDF tools both online and as a downloadable desktop application. The online version covers merging, splitting, compressing, converting, and editing, while the desktop version adds a virtual printer so you can create PDFs from any application. There's also OCR for scanned documents, page numbering, and a tool for comparing two PDFs. Everything is free with no watermarks and no usage limits.

The desktop app runs on Windows and can work offline, which is useful if you don't want to upload documents to a website. The interface is a bit dated compared to newer tools, but the functionality is solid and the price is hard to argue with. For anyone who needs a reliable PDF toolkit without paying for Adobe Acrobat, PDF24 is worth installing.