  The code we describe (FLY) is a newly written code (using the tree N-body
method), for three-dimensional self-gravitating collisionless systems
evolution. FLY is a fully parallel code based on the tree Barnes-Hut algorithm
and periodical boundary conditions are implemented by means of the Ewald
summation technique. FLY is based on the one-side communication paradigm to
share data among the processors, that access to remote private data avoiding
any kind of synchronism. The code was originally developed on CRAY T3E system
using the logically SHared MEMory access routines (SHMEM) but it runs also on
SGI ORIGIN systems and on IBM SP by using the Low-Level Application Programming
Interface routines (LAPI). This new code reaches good performance in all
systems where it has been well-tested. This performance allows us today to
consider the code FLY among the most powerful parallel codes for tree N-body
simulations. The FLY version 1.1 is freely available on
http://www.ct.astro.it/fly/ and it will be maintained and upgraded with new
releases.
