Limewire is a file sharing client written in Java and available for many platforms (Windows, Macintosh Classic, OS X, and several Unix flavors). Also, Windows clients are available in many languages (English, Spanish, Chinese, etc).
LimeWire is one of the oldest Gnutella clients (it's been around since late 2000). It is written in Java. In September 2001, LimeWire was released as open source software under the GPL. Official development on the client continued, though. At one point, the official free version provided for download contained advertising and spyware, with a "Pro" version for $9.50 that was ad-free and spyware-free. As of January 2007, the free version claims to be ad- and spyware free, but with fewer features than the pro version. Numerous free (and legal) forks of the project also exist.
The LimeWire group actively participates in The Gnutella Developer Forum and has played a key role in designing such protocol improvements as HUGE and QRP. LimeWire can be considered one of the most advanced Gnutella clients.