Zelune is another proxy script written in PHP. Its history is quite long; but it has not widely used, partially due to its unclear license terms. It is free, but the license terms was never clearly stated in the download page or with in the script.
Also, there are two confusing variations: zelune.com and zelune.net. Now a new member, Phphantom scripts (which was released under GPL), was added to this family in 2008. The website claims that Phphantom scripts will merge with Zelune script; but it seems it is not available at this time yet.