The Serge project is a monorepo, we use Yarn Workspaces for our monorepo needs but that is augmented by it's coexistence with Lerna.
Our Directory structure is based on the directory structure recommended by Lerna and looks like this. All packages are found in the /packages folder.
Packages can be thought of as standalone apps, however, they can also talk to other packages inside the monorepo. For the most part, we will not be creating new packages, however, where it is appropriate, new packages can be made. Each package should be named in snake_case syntax and must contain at a minimum a package.json file and a README.md file which has been completed to a good standard (see here for more information).