Can I launch other apps on the user's device from within a Screen?

Launching other installed apps is possible only if the target app supports custom URL schemes.

Basically this allows you to use the "Open Web Browser" interaction with an app-specific URL as the parameter.
e.g. fb://requests should open the Facebook app if its installed.

You can also pass values into the target app if the app supports this.  
This is achieved by using formula syntax to dynamically generate the "Open Web Browser" parameter.
e.g. twitter://user?screen_name={{myfieldname}} should open Twitter to the given user's page.

A simple way to test custom URL schemes easily by simply pasting these into your device's web browser - normally this is sufficient

For some reason, custom url schemes are not always readily advertised by app makers.

So we recommend you also search the web to find out if there are any URL schemes supported by your target app - use a search phrase like "custom URL scheme <target app name here>".