Trac has a [patch|http://trac.edgewall.org/attachment/ticket/4356/trac_wiki_creole-r4428.patch] which partially supports Creole (bold, italics, links).

*[TracWiki page about Creole|http://trac.edgewall.org/wiki/WikiCreole]
*[TracWiki Ticket|http://trac.edgewall.org/ticket/4356]