Arena's primary purpose is to be a testbed for new features of the
web. In the past, we have implemented HTML3 features including tables
and math. Currently, style sheets are in focus along with new graphics
formats such as PNG. Also, Arena is a testing tool for the W3C
Reference Library. The library provides a common platform which
will ensure future compatibility on the web. If you are a
browser vendor, it will save you time.

WWW: http://www.yggdrasil.com/Products/Arena/