Started in Aug 1991, (formerly is a fully automated electronic archive and distribution server for research papers. Covered areas include physics and related disciplines, mathematics, nonlinear sciences, computational linguistics, and neuroscience.  
Users can retrieve papers from the archive either through an on-line world wide web interface, or by sending commands to the system via e-mail. Similarly, authors can submit their papers to the archive either using the on-line world wide web interface, using ftp, or using e-mail. Authors can update their submissions if they choose, though previous versions remain available.  
Users can also register to automatically receive a listing of newly submitted papers in areas of interest to them, when papers are received in those areas. These listings are sent by e-mail.  
In addition, the archive provides for distribution list maintenance and archiving of TeX macro packages and related tools. Mechanisms for searching through the collection of papers are also provided.  
scientists can find many publications even the ones that havent been published yet..good stuff  
potatono: Nice, it uses the linkfilter concept to some degree.  
Why was it once a .gov site though?  
miro: no clue but it is least has some mirror over there..probably they have an urgent need to know about everything?;)