You can download Oppa for free on your AppStore or Google Play (Search for Oppa). Once installed, you have to connect to your Facebook account to login into the app and create your user.
As I am writing this, you'll need an invitation to join the group from an existing user.
The interface is nice and you can post photos and videos (up to 60 seconds). There is not a lot of people right know but enough to keep you busy once in a while. If you like some post, you can like it, shared 0.10$ with the owner and even offer a virtual gift ranging from 1$ to 99$. It's a micro-blogging social network where fans can show their appreciation with real money.
I've been testing Oppa for the last week and I received up 6$ from others for some pics and videos I posted.
If you want to try it, you can use my account as a referrer: PBALLEUX
Let me know in the comments what you think about Oppa.