Blocks Templater is a web based application for creating and editing templates to be used for webpages or email campaigns in Blocks.
Like Blocks itself it requires no software to be installed.
It enables those with knowledge of html and css to create Blocks templates from standard html or from scratch.
With it you can create regions for both text and images that are editable by the client and set up flexible navigation or common regions, like footers.
You can view the technical documentation here.