As of 2009/09/16, the Helma website supports Markdown as wiki markup format. By default, the old Gobi markup is used. To write a page using Markdown, check the "Use Markdown" checkbox at the bottom of the edit form.
The helma.org markdown formatter uses an extension for wiki links. Wiki links are like ordinary Markdown links, except that you don't provide a URL. Just use the page name as symbol in the square brackets and it will be resolved as wiki link.
[Test Page] turns into a link to Test Page. You can use something other than the page name by writing something like
[random link text][test page].
At some time in the future when we have converted most existing pages, Markdown will become the default page format on helma.org.