StegFS
StegFS is a free steganographic file system for Linux based on the ext2 filesystem . 
<triplet> StegFS <subj> free <obj> instance of <subj> steganographic file system <obj> instance of <subj> Linux <obj> operating system <triplet> Linux <subj> free <obj> subclass of <triplet> ext2 <subj> Linux <obj> operating system