Cookfs is done as part of cookfs/cookit project - which aims to create a more space-efficient tclkit-like solution without C++ dependencies and limitations of read-only access.
Its home page is: 
Cookfs is a Tcl virtual filesystem using a compressed archive format to allow embedding multiple files in an archive that Tcl scripts can access directly.
It is optimized for storing Tcl packages (allowing around 10%-20% smaller sizes ratio than mk4vfs while still using zlib compression), small, fast and integrated with Tcl.
It is designed only for use in Tcl and provides multiple optimizations especially for delivering Tcl-based standalone applications.
Currently it works on top of tclvfs and can work as both pure Tcl and Tcl+C combination - where Tcl+C is obviously faster, especially for large number of files (i.e., above 100k).