The best open source software in the category Communications:
FileZilla
FileZilla is a cross-platform graphical FTP, FTPS and SFTP client a lot of features, supporting Windows, Linux, Mac OS X and more. FileZilla Server is a reliable FTP server for Windows.
PortableApps.com
PortableApps.com allows you to carry your favorite computer programs and all of your bookmarks, settings, email and more with you on a portable device (USB flash drive, iPod, portable hard drive, CD, etc) and use them on any Windows computer.
DC++
DC++ is an open source client for Windows for the Direct Connect / Advanced Direct Connect network.
Direct Connect allows you to share files over the Internet without restrictions or limits. The client is completely free of advertisements and has a nice, easy to use interface. Firewall and router support is integrated and it is easy and convenient to use functionality like multi-hub connections, auto-connections and resuming of downloads.
Shareaza
Shareaza is a very powerful multi-network peer-to-peer ( P2P ) file-sharing client supporting Gnutella² ( G2 ), Gnutella ( G1 ), eDonkey2000 ( eMule ), DC++, HTTP, FTP and BitTorrent protocols for Windows (or Wine).
