Wekan uses GFM (Github Flavored Markdown). We use the following project that ports GFM to meteor: https://github.com/wekan/markdown with updated newest markdown, that is fork of https://github.com/perak/markdown.
Note: In order to use gfm checklist and other v0.28+ features, you need Wekan v2.61+.
List of guides (from web archive):
Where can I use the markdown?
- Card name.
- Board name - Works on board view only.
- Card description, list and task list.