Canvas does not have a Wiki tool, but you can create a course wiki by creating a Page and allowing students to edit it. Currently, there is no way to grade student contributions to this Page, so this should only be used as an informal study aid and not a formal course requirement.
Please note: Canvas does not give any warning that another user is editing a Wiki at the same time as you. From our testing, it appears that if two users edit a Wiki at the same time, it will only save the data that is submitted first. This means that users can lose a lot of data and waste time editing group pages by overwriting each other's data. One possible way around this is for users to type up and save their wiki contributions in Microsoft Word, then copy and paste them into the Page. This way, even if their work is lost in Canvas, they can easily copy and paste the information again.