For the Unix people there's the wml-tools which is  available at http://pwot.co.uk/wml/ which includes cool stuff like a WML bytecode compiler and decompiler.
   
Angus at Zygo WAP (angus@z-y-g-o.com) has developed a subclass of LDS's CGI.pm for WAP methods and WML output for use with Perl, and he's also working on a pipelineable WML compiler. All available at Zygo WAP Tools.
 
RCP Distributed Systems has a command line WML Compiler available at http://www.rcp.co.uk/distributed/Downloads. The compiler runs under Windows9x.