Are there any advanced apps that are built using fabric js?

http://printio.ru/ is the one of best one, what kind of advance apps you are looking for ? check out the discussion on google groups https://groups.google.com/forum/?fromgroups#!forum/fabricjs you will get some idea

We built Fabric specifically to power design editor on Printio.ru. It's used by 1000+ visitors daily.

From other big sites there's easel.ly — visual themes creation tool. Also mywallsticker.de, scrollkit.com, and others.

Large sites that using FabricJS are listed here https://github.com/kangax/fabric.js/wiki/Who%27s-using-Fabric