I can think of two apps: Musing and Steemmonster
I actually marketed steemmonsters to a friend. Told him it was a game where he could sell his characters if he liked (or got bored of the game)
for musing, I'll basically say 'get rewarded for asking and answering questions'
To market anything, you make those you're marketing to see the benefits of the product you are market. No one would patronize your products unless they're made to see the benefits. So the easiest way to market any steem app to people outside of steemit is by stating the advantages of having such apps and how the services the app is offering would help them improve such aspects of their lives or daily activities. It's that simple!
@Jesmin30, In my opinion, it's really easy because, we all know that Centralised Platforms are not rewarding their users and people are spending hours without any returns, so for sure people will going to feel excitement towards the aspect where they can earn rewards while doing their favourite activities. Stay blessed. 🙂