Custom Screens strategy (☰ → Strategies) lets you add multiple Smart Lists into one view.
Some workflow snippets (☰ → Workflow Library → Snippets) are actually Custom Screens and here you can see the "Communication" one that combines "Calls, "Emails" and "Contacts" smart lists.
To set up a custom screen, go to the strategy settings and click on the "Add Screen" button after which you can choose how you want that screen to be displayed.
After you do that, you should give it a name and then you can add smart lists to it. Additionally, you can pick an icon for each smart lists you add to it which will then be displayed in the main view.
Once you create a custom screen, you need a way to access it. You can add it to one of the following strategies:
Here's how to link it with a custom square: