FUSE is a user-mode filesystem library for linux. It needs my standard libraryto run. Obviously, you'll need to install FUSE as well. I've run it under the 2.6.3 linux kernel.
Here's an example program. It creates a non-hierarchical filesystem which supports a subset of the posix filesystem semantics.
You will need to read the FUSE documentation to make use of this. The scheme interface is fairly thin: it's a one-one mapping of operators from the C library with the numeric made symbolic.
Performance is not very good.