SNNS (Stuttgart Neural Network Simulator) is a software simulator for neural
networks on Unix workstations developed at the Institute for Parallel and
Distributed High Performance Systems (IPVR) at the University of Stuttgart. 
The goal of the SNNS project is to create an efficient and flexible
simulation environment for research on and application of neural nets.

The SNNS simulator consists of two main components:

1) simulator kernel written in C
2) graphical user interface under X

The simulator kernel operates on the internal network data structures of the
neural nets and performs all operations of learning and recall. It can also
be used without the other parts as a C program embedded in custom
applications. It supports arbitrary network topologies and the concept of
sites. SNNS can be extended by the user with user defined activation
functions, output functions, site functions and learning procedures, which
are written as simple C programs and linked to the simulator kernel.

The graphical user interface XGUI (X Graphical User Interface), built on top
of the kernel, gives a 2D and a 3D graphical representation of the neural
networks and controls the kernel during the simulation run. In addition, the
2D user interface has an integrated network editor which can be used to
directly create, manipulate and visualize neural nets in various ways.

WWW: http://www-ra.informatik.uni-tuebingen.de/SNNS/