Fontli is quite a few months old already but I only just discovered the app the other day. It's an Instagram-like social network which is purely targeted at typography lovers.
The idea behind the app is to take a picture of a form of typography you've seen and then upload it to the app. People can then like or comment on your picture, just like on Instagram. Fontli though also has some other features.
It has a popular tab but along with the popular tab you also get a limelight tab and "recently spotted" tab. The limelight tab highlights members using Fontli and uploading great content. The "recently spotted" tab is where you can find names of actual fonts which have been spotted by members. You can check out the pictures within which the font has been spotted which is also very neat.
You can actually find some pretty awesome fonts which you may not have known of before. You can see them in use which can easily provide you with inspiration on where you might want to use a font.
With the app still relatively new and very niche there isn't a huge amount of members. But the app definitely does have the feel of a proper social network. I can't see the app being anywhere near the size of Instagram purely because of how focused it is, but that's the point, it's made exclusively for people who love typography.