List Layouts for Trello
The List Layouts for Trello extension adds a button to your Chrome toolbar allowing you to toggle the Trello board layout from horizontal to grid to vertical by clicking the icon.
Download and install the extension from here: Chrome Web Store - List Layouts for Trello
Pull requests welcome. Take a look at the Issues page for features needing attention. Post on an existing issue or create a new issue if you have questions. It's a small extension, easy to grok if you have some web development experience.