First of all, it is important to understand what FUSE is. FUSE - FileSystem in Userspace - helps users without any privileges to create their file system without a necessity to write code in a kernel space.

This is possible because the filesystem code runs in userspace. And the FUSE module is just a bridge between the kernel API and your code. FUSE was officially included in the Linux source tree in 2.6.14.

So, you can easily create your own filesystem (here is the simplest example). There are a lot of areas where you can use it. For example, you can quickly write a FS where Github or DropBox would be the backend.