@sysads Its called cross-promotion. I know that Ketchapp has a program called Ketchads that is not live to everyone right now. But you can look into TapDaq. They have an SDK that is easy to add and allows you to cross promote your games. www.tapdaq.com
I believe most of them are using the feature from TAPDAQ. It launches a new app in their games that already has many players. @sysads