I write ExpanDrive, http://www.expandrive.com - which mounts SFTP/S3/Dropbox/Openstack Swift/Google Docs/Box on Mac/Windows & soon Linux all in Python/FUSE.
Ctypes is the way to go for interacting with libfuse. Even better would be speaking the FUSE protocol directly to /dev/fuse*, but is rather complicated by our Windows support.
Oh, congrats, I used ExpanDrive when I was using Windows and I remember it being the best S3 client I had tried. I'm very excited for Linux support. Feature request: please make sure it supports ACLs properly, nothing else I've tried does. I'll set a folder as world-readable, but, when I upload a file into it, the file won't have inherited that permission and I have to go and do it manually every time...
For those who don't know the space, ExpanDrive used to be SftpDrive. I've been recommending it for years to people who are not technical for accessing sftp shares and have never been let down. Thanks for a great product and sharing some detail about how it works.
Nothing open-source, unfortunately. I originally wrote a Windows fuse-like filesystem driver that we used in our 1.x product line, but that was a lot of work to maintain and have since switched to CBFS https://www.eldos.com/cbfs/ - which I wrote a libfuse binding for that we directly mount through via ctypes. They are actually in the process of formally building out FUSE support for CBFS but it's not officially supported.
I wouldn't ship a loosely maintained open-source kernel driver to paying customers. You can get CBFS for less if you're an indie shop, but the don't directly publish the price anymore. Compared to spending a year writing a gross Windows filesystem driver or hiring somebody to do it CBFS is amazingly inexpensive.
Ctypes is the way to go for interacting with libfuse. Even better would be speaking the FUSE protocol directly to /dev/fuse*, but is rather complicated by our Windows support.