I have posted a preview version of UsbFat here on GitHub.
The library has been tested with Uno, Mega, and Due using this host shield.
The library can also be used with the Mega ADK board.
I am working on support for Teensy 3.x using this mini host shield.
The library can be used with USB flash drives and USB hard drives that are formatted FAT32 or FAT16.
There are four example programs.
Here is output from UsbDriveInfo using a hard drive on a Due board.
UsbFat version: 20141220
Type any character to begin
Volume Size: 499982.60 MB (MB = 1,000,000 bytes)
Volume is FAT32
Determining free cluster count - please wait.
freeSpace: 499982.13 MB (MB = 1,000,000 bytes)
This hard drive has 15,258,258 clusters so scanning it for free space takes a while but works.
The other examples are
UsbFatBench - A read/write benchmark.
UsbFatDemo - A simple Demo program.
UsbLogger - A simple modifiable data logger.