MyNapster is one of the many file-exchange clients for the Gnutella network and it does the ususual things the usual way - you share your own files (music, videos, images, programs - whatever) and download files shared by other people on the network, you can search for the files you want, resume interrupted downloads, limit the bandwidth for upload/download etc. It does have a few unique features though: a built-in chat client for use on the IRC servers within the Gnutella network, and a graphical node list - a map-like representation of the way the signal goes to and from your machine through the network. I can't call these features too useful, but they work well.
This Gnutella client has a pretty ugly single-window interface, but as far as I know, all Gnutella clients are ugly. MyNapster also comes under full GNU license and its developers offer no warranty for it at all. It also lacks the brilliant network health tools of Limewire. But in actually getting the things done MyNapster outperforms not only Limewire but also all other Gnutella clients I've seen - under the unpleasant interface there is a very fast, very stable file sharing program. Choose it if you care for performance vastly more than for looks.