Sumatra PDF is a slim, free, open-source PDF viewer for Windows. Portable out of the box. Sumatra has a minimalistic design. Simplicity has a higher priority than a lot of features. It's small and starts up very fast.
It's designed for portable use: it's just one file with no external dependencies so you can run it from external USB drive.
7-zip is an open-source file archiver with high compression ratio with support for 7z, zip, gzip, tar files etc. It has been found that the compression ratio of the new 7-zip in the 7z format is lot better than the best known compression softwares like Winzip and WinRar!!
This is an awesome P2P file sharing software, probably the fastest one in its category and the best feature is its open-source!!
Using Sababa DC you can exchange any files over direct connection protocol. This software is a client free of spyware. Using Sababa DC you get the power over DC networks. You have the right to create your own servers and communities. Check out itsfeatures.