s3fs is a FUSE file system that allows you to mount an Amazon S3 bucket as a
local file system. It stores files natively and transparently in S3 (i.e.,
you can use other programs to access the same files). Maximum file size=64GB
(limited by s3fs, not Amazon).

s3fs is stable and is being used in number of production environments, e.g.,
rsync backup to s3.