Stable multi-threaded programming (Roxen has been multi-threaded since 1994).
Mostly written in an interpreted, object-oriented, language - Pike:
Easy to program and extend. Just imagine if you could code extensions to the Apache core in PHP or Perl.
No buffer overflows, segmentation faults or any other problems of that nature.
RealNetworks is still using Roxen 1.3 as their main web platform for its stability and speed.
Low level API available for end-users.
RXML tags.
Lots of modules.
Backwards compatible with Roxen 1.3.
Different. If you are a Linux or BSD user for some time you already know the most used is not always the best.
Caudium won't run under win32 (thus letting us more time for useful things). However some people are trying to port it using cygwin without code modification.
Embedded PHP4 support.