Vibe Streamer is a fun way to share your music with your friends. Although it's basically a file server, you don't have to spend too much time with configurations.
You can add groups to have different settings and other kind of shared music for each group: your co-workers, your friends, your family. After adding groups, you should create usernames and passwords for each person who will listen to your music. If you create an account that will be used by more than one person, change "Max number of users" in settings. Then add your shared directories, select your IP address and start the server. You can now invite your friends to visit http://your-ip-address:8081, replacing your-ip-address with your IP. They can browser the directories, choose the music they like and play it as a stream.
Vibe Streamer's client is a web page that works with any browser, but the server is only available for Windows. Another limitation is that you can share only MP3 files. As all you do is stream the content of the files, your friends won't get the raw MP3s, so you're not doing anything illegal.
Remember to keep the server functioning in order to let your friends listen to the music.