I'm very interested to see all the new applications that are starting to be built on top of lightning.
One area in particular that I think will be very popular is decentralized social media/chat/file transfer. In that area, I've found
Sphinx,
Juggernaut, and
Impervious. They look very promising, you can even monetize your own messages/data out of the box.
Another area that I think will be very popular is to use lnurl-auth as login instead of remembering passwords for websites. Here's one example of that:
https://lightninglogin.liveBy the way, this might be a good time to reserve your own
lightning address.
For game developers,
zebedee is offering an easy to use api to make money be part of the game by making micro-payments with lightning.
If you've seen any other interesting application running on top of lightning, make sure to share it here.