A command-line Gnutella program, powerful in its simplicity.
To get started, download and install gnut on your operating system of choice. The usual ./configure ; make ; make install recipe almost always works. You might want to touch ~/.gnutrc if you know what it does -- otherwise don't worry about it.
When you run gnut, the first thing you'll want to do is type "help" for a list of commands. I find it useful to type mreply to monitor the replies coming in from other people's searches; that will give you an indication of whether you've gotten connected to the network yet. It can take a few minutes, so be patient.
To find files, type find keywords. For example, "find mp3" will get you lots of files with "mp3" in their name. Typing "find preteen mpg" will get you lots of trouble with your network administrator, police, deity, etc.
You'll get a numbered list of available files. Type get numbers ("get 1-3,7,9-13") to request files, and use info to check on your connections. You'll probably want to stop the requests that aren't getting anywhere. Keep in mind that the numbered lists of files and transfers are separate from each other, and that they're generated each time you type find or info.
That's about it. Files will go into your current directory, or in download_path if you've set that variable.