OpenDX is a very capable package and it runs on most UNIX platforms. A software environment for analyzing data from numerical simulations. FAST is free and includes source code. Unfortunately it only runs on SGI workstations. VU is available for free to Universities.
Companies have to pay an annual fee.
VU runs on most Unix platforms. The site gives further information and has a tutorial and a manual available online. A free package developed and maintained by Pedro I. Espina . Uses proprietary Silicon Graphics routines so it will only work on SGI's. Only handles 2D databases.