DEVONThink. Drafts. Dendron. All of these productivity powerhouse apps support Wikilinks. And with version 6, so does iA Writer.
The interesting part of how iA Writer uses Wikilinks is that it seems to find any Markdown file on your Mac. In apps like Workflowy, and those I listed above, Wikilinks will only search within themselves. Workflowy Wikilinks will only reference nodes within Workflowy, for example, and likewise with Drafts. But on my Mac (and iPad), iA Writer will look outside of it’s own iCloud folder to any location you’ve added to iA Writer’s Locations feature in the sidebar. So if you add your Desktop as a location, iA will look for documents there once you type “[[” to open a Wikilink.
Wikilink in Action on iA Writer
You can only link to text files that iA Writer will read and edit, however; Wikilinks can’t point to PDFs, for examples. (You can make a Markdown link and point to the file using Hook, however).