Soulseek

Soulseek is a filesharing program that has been around since about 2002. It's invaluable for finding rare, hard-to-find, bootlegged and indie label music. Soulseek is a tool for musicians to get their music heard on a large scale. All you have to do is install and add your shared & incoming folders and you're set. Enjoy this great music community and be aware of what you share and download.

If you're an artist of any kind this program will be invaluable to you. I find it especially useful for talking to friends and family who live far away and who live abroad. You can chat with your mom while uploading your latest song, painting, photo etc to her computer. When the download completes she can open the file while not missing a beat on the chat. Perhaps you're a filmmaker and you want to spread your work around to get opinions on it... here you go. Soulseek is a great community of great people, please respect everyone when you get on and especially in chat rooms if you visit them. Oh that reminds me! Another great thing about Soulseek is you can make your own chat room and even make it private if you want, you can have just your friends in one room and just your family in another room and have all of them in a third room, with all rooms moving at the same time! All this while uploading that family photo to your mom, and don't forget to send her the video of her grandchild's first steps and the audio file of the kid's first word!

From their site:
Soulseek® is a unique ad-free, spyware free, and just plain free file sharing application.
One of the things that makes Soulseek® unique is our community and community-related features. Based on peer-to-peer technology, virtual rooms allow you to meet people with the same interests, share information, and chat freely using real-time messages in public or private.
Soulseek®, with its built-in people matching system, is a great way to make new friends and expand your mind!
Soulseek® does not endorse nor condone the sharing of copyrighted materials. You should only share and download files which you are legally allowed to or have otherwise received permission to share. By using this network you agree to this and the other rules which are linked to from this page. The intention of Soulseek® is to help unsigned and/or independent artists find a place in the ever-growing music industry, in a place where discussion and the creation of music can take place. Use of this network for illegal or infringing purposes is not permitted. Please share responsibly and help make Soulseek® a place where all artists can find a common ground.