Missing “Grid Layout” and “Flat Layout” homepages on “Mellisa” demo site
In the meantime, if you have the Mellisa theme …
Under: Theme Settings > Custom Settings > Post Listings
You can choose between “List view” and “Grid view” for Front-page, tag page(s), and author page(s).
And you can set how many grid columns you want. 3 seems to work well.
So if you have say at least 6 or 9 posts, you can see how grid view looks and behaves.