1) eDonkey / Overnet
http://www.zeropaid.com/edonkey/
eDonkey/Overnet is a state-of-the-art P2P file sharing software system. Especially popular in Europe, the two P2P networks eDonkey and Overnet combined support a large base of users and files. The eDonkey P2P client connects to both networks; the Overnet client is being merged into future releases of eDonkey. eDonkey runs on Windows, Linux and Macintosh computers. The free version of eDonkey contains embedded advertising but none of the dreaded "spyware" found in some free file sharing software.

2) Shareaza
http://www.shareaza.com/
Shareaza is an up-and-coming P2P file sharing program. This client offers an extremely powerful search engine capable of connecting to multiple popular P2P networks including eDonkey, BitTorrent and Gnutella. Shareaza file sharing software includes intelligence for detecting fake and/or corrupted files. The free Shareaza download also contains no ads or spyware. As the installed base of Shareaza client users grows, expect Shareaza to become an even better P2P file sharing program.

3) WinMX
http://www.zeropaid.com/winmx/
WinMX offers a large P2P file sharing network and a feature-rich client program that has evolved over years of development. True, WinMX has a reputation for being complex and more difficult to use than some alternatives. However, WinMX also provides power to users in managing their downloads, and it offers a wide selection of music (MP3) files. Some WinMX users report waiting in long queues to download popular files. WinMX software runs only on the Windows family of operating systems.

4) BitTorrent
http://www.bittorrent.com/
BitTorrent is another free P2P software application. It has attracted a loyal following among those interested in sharing movies and television programs. The offical BitTorrent P2P client generally does not support bandwidth throttling, meaning that it will tend to monopolize a network connection and not allow surfing the Internet or otherwise utilizing the network while files are being downloaded or uploaded. A freely-available alternative BitTorrent client overcomes this limitation.

5) Limewire
http://www.limewire.com/english/content/home.shtml
The Limewire P2P file sharing program connects to the Gnutella P2P network. Limewire client software is widely recognized for its clean user interface that does not contain adware. Sometimes billed as the "fastest file sharing program," Limewire claims to offer relatively good search and download performance. Free Limewire software downloads are available for Windows, Linux and Macintosh operating systems. Limewire Pro pay clients also exist.

6) eMule
http://emule.org/
The eMule project started with the goal of building an improved free eDonkey client. eMule has achieved a large user base, connecting both to the eDonkey P2P file sharing network and a few others. It contains no advertising, and its software base is well-maintained by an open source development team. The chief limitation of eMule’s P2P file sharing program is its speed: eMule typically performs downloading much slower than other P2P clients.

7) Ares
http://aresgalaxy.sourceforge.net/
Ares is a full-featured free P2P network with its own file sharing programs including Ares Galaxy. Ares clients support decentralized music and other file sharing and include a built-in chat service. Ares strives to offer the simplicity of Kazaa clients with no adware and fast connection times.

BearShare
http://www.bearshare.com/
The BearShare P2P file sharing program is a popular free software client for the Gnutella P2P network. Both free and pay downloads of BearShare file sharing programs exist.
References :

I downloaded for free they’re toolbar that allows me to upload whole folders or many files all at once very quickly, it is also free to use their service.
References :