Lklvfs is a project mainly written in C, it's free.
(old project)
Linux Filesystem driver for WINDOWS
To build LklVfs you'll need LKL and Mingw. To test it you need mount tools by Matt Wu (http://ext2fsd.sourceforge.net/resources/resources.htm) or the filedisk tool (http://www.acc.umu.se/~bosse/) if you want to mount a image that contains a Linux filesystem. To see a list of bugs ( fixed or not): http://bugs.launchpad.net/lklvfs/